Others have covered the documentary sources very well. I'd like to draw attention to another way of answering this question: the Hitler-Mannerheim recording: https://en.m.wikipedia.org/wiki/Hitler_and_Mannerheim_recording

This is the only known recording of Hitler having an unscripted conversation. It was made without his knowledge. An English transcript is available here.

https://civilianmilitaryintelligencegroup.com/19880/transcript-of-a-recording-of-adolph-hitler-and-carl-mannerheim

I haven't verified it, but on face value:

1) Hitler talks a lot. It's 11 minutes and Mannerheim hardly gets a word in. Unsurprising.

2) More surprising: Hitler seems worried, anxious, maybe even depressed. It goes without saying that he had good cause to be concerned by June 1942. However, he always projected an insane level of self-belief. I always thought he was crazy enough to believe he could never lose, but maybe he knew he was scuppered and there was absolutely no way out of it.

Q What was Hitler like in private?

We cannot know!
The vast majority of material available that otherwise might shine some light on this is highly unreliable.

Q That being said, we also know that Hitler's public image was very carefully maintained.[…] Do any unbiased firsthand accounts exist of Hitler's general personality and demeanor[…]?

This care for image continues to this day. And that's the reason we do not have 'unbiased' accounts.

Almost all those movie snippets we have been shown a trillion times by now were crafted and selected by the Nazi propaganda machine. We see him in uniform, but not in pyjamas. Almost all recollections or memoirs involving him are not from anything 'private' but social occasions at best. At those he maintained an image, and those reporting it did that as well. They maintained an image of him –– and of themselves. Of course the typical distortional effects of human memory only add on to this.

This gets worse for English-only speaking inquirers into this, as virtually all attempts at researching this is severely handicapped by outright bullshit published as fact, even by major biographers who are otherwise reliable and generally respected. Be that Kershaw, Toland, Irving, Pyta, Ullrich or Fest they all jump into the trap for this aspect, with a wryly grin.

It is really egregious how uncritical "Hitler in private" stories are told.

Most people asked will point to "Hitler's table talk". A collection of censored, redacted and invented material in which fact and fiction are indistinguishable. The German version is largely worthless already, but the quality deteriorates in the French and ever more so in the English versions.

Some will point to Speer's memoirs. A notorious liar who after 1945 seems to have never written down anything truthful in his books which were not much more but a utility for his own image.

Other accounts may want to claim that "ah, but the story his own private secretary tells" must be genuine, reliable, close to the source, really 'private'. That is not the case.

From all these sources we have a puzzle in which the pieces are largely missing and those remaining have pictures that faded, were overpainted, exchanged and from all remaining the edges are mostly broken off.

Example 1: Table Talk

"Hitler's Table Talk", in all its incarnations had its content commissioned and authorised allegedly by Bormann and was then published in German by an actual witness of these events, Henry Picker, in a very limited edition.

A first review of that book appeared to be not very convinced of its content:

Alfred Vagts: Review of "Hitler's Tischgespräche im Führerhauptquartier, 1941-42. – By Henry Picker. [Im Auftrage des Deutschen Instituts für die Geschichte der nationalsozialistischen Zeit, geordnet, eingeleitet und veröffentlicht von G Ritter.] (Bonn: Athenium Verlag. 1951. pp463.)":
[…] They are not stenographic notes but memorandums written postprandially.
Such grading raises once again the question of the true reproduction of Hitler's utterances, recalling to the reviewer the time when, as a history student in Munich in the early I920's, he went together with friends to NSDAP meetings and afterwards tried to agree with them on what the speaker of the evening had actually said: there was never, within an hour after the meeting's close, any firm agreement as to the content of the speeches, though all of us were trained to observe and note down historical facts. Neither the victims nor the observers of the Pied Piper seemed able to reproduce the words to the tune they carried away in their ears, though not a few of them might notice the palpable errors and intentional falsehoods in the oratory. These errors are here again, not only numerous factual mistakes, as Professor Ritter warns the reader, but many which seem calculated to impress an audience by their false conciseness. (On one page an overpaid actor's salary is given as 3-4000 marks per month, on another the same man's earnings are 3-4000 marks per evening [pp. 35, 386]; "75 per cent of the German emigrants to Australia died en route" [p. 310]; "Venice's constitution lasted exactly 966 years" [p. 2041. One wonders why not 1100 years, from the first doge to the end of independence in 1797.)

It is therefore entirely in doubt what was actually said, and no-one can be sure whether Picker was accurate, whether and much Bormann was smoothing things over or whether Hitler himself changed anything when glancing over it to authorise it.

But as can be seen from the dates this volume is supposed to cover it is not the entire basis for is this book of "Hitler said that". It gets so much worse for the English version, published much later!

And this 'source' also has a colourful publication history:

Richard C. Carrier: "'Hitler's Table Talk': Troubling Finds", German Studies Review, Vol. 26, No. 3 (Oct., 2003), pp. 561-576:
What is the Table Talk?
The Table Talk is purportedly a transcription from notebooks written in shorthand by at least two secretaries to Hitler, Heinrich Heim and Henry Picker, who were instructed by Hitler's right-hand man Martin Bormann to record for posterity whatever Hitler said in his bunker in Berlin, usually during meals or tea. In addition to official matters, they recorded things he said off the cuff, each logged by date and time (like "morning," "afternoon," or "evening"). So far all accounts agree. Beyond this is some confusion that an enterprising historian will some day have.

That may be difficult, since much is said by Genoud and Trevor-Roper without a word as to how they know it. No sources or documents are cited.
One might readily question the authenticity of such a text, given the conflicting versions and questionable chains of custody in this case and the abundance of other forged works purporting to reveal the secret thoughts or plans of Hitler. But it is likely the notes were real. There are two completely independent manuscripts, and a fragment of a third; and all agree in such a way as to corroborate the existence of a genuine original. The fragment consists of forty-two typed pages in the Adolf Hitler Collection at the U.S. Library of Congress, which are probably authentic. Scribbled in handwriting atop the first page of these is the brief remark: "Found by Mr. Jos. Schrasberger, München, Herzog Wilhelm Straße 4." This is probably part of the lost copy of the Bormann manuscript (discussed below). Finally, Werner Jochmann's edition of the text includes an introduction citing notes and letters confirming the Table Talk was indeed being made and collated during the war.

Picker, of course, was an eyewitness to this affair, and says in his first introduction (33-34) that Heim had been authorized by Bormann to go beyond his official duty to transcribe Hitler's spoken orders and decisions and to include whatever else interested him, and this authority passed to Picker during Heim's brief absence. Picker says Hitler actually looked over his record on occasion and approved it as accurate, yet didn't realize how often these notes were being taken.
He also reports that the official notebooks collated by Bormann were lost in the "confusion of the surrender." These would turn up a year later in Genoud's possession, and some pages from a copy of this apparently ended up in the Library of Congress. But Picker retained his own original notes and those made by Heim before him.

Trevor-Roper's edition claims to be working from a version of the notebooks extensively edited and collated by Martin Bormann, called the Bormann Vermerke ("Bormann Notes"), which until recently existed only in the private collection of François Genoud. Genoud relates in his 1952 preface that the thousand-page monstrosity had a note at front in Bormann's handwriting: Bitte diese - später äußerst wertvollen - Aufzeichnungen sehr gut aufheben, "Please preserve with the greatest care these notes of a capital interest for the future" (Jochmann publishes a facsimile of this note opposite his title page). According to Jochmann's introduction, these were to be the "official" notebooks, collated and edited from the originals by Bormann and published as a definitive party manifesto for the victorious Reich. Unlike Picker's, the Bormann text continues to 1944. Since Picker received his copy of the notes from Heim upon replacing him until Heim returned, he did not have access to the remaining notes taken after this tenure.

Jochmann and Trevor-Roper (in the preface to his third edition) both relate (among many other details) that the Bormann-Vermerke was sent piecemeal from Bormann to his wife Gerda. Another copy reportedly went to an office in Munich, which was likely destroyed by allied bombing, apart from the pages recovered by Schrasberger. Gerda fled to Italy with her collection of the notes in 1945 and died there in a detention camp in 1946. A local Italian official then acquired the manuscript, which he sold to Genoud around 1948. That manuscript is the basis for Jochmann's text, as well as Genoud's and Trevor-Roper's translations.

Which Version Should We Trust?
There are so many published versions and editions of these notes I gave up attempt to track them all. In general, there are four major versions, each with its ow advocate: Henry Picker (1951, 1963, 1976), Francois Genoud (1952), H. R. Trevor-Roper (1953, 1973, 2000), and Werner Jochmann (1980). Of these only two offer the original German (Picker and Jochmann). Genoud, a Swiss banker a lifetime Nazi, offers his own French translation. Historian Trevor-Roper presents the English translation of R. H. Stevens and Norman Cameron.

From the isolated comparisons I made, Trevor-Roper's English appears to be an almost verbatim translation of Genoud's French. Yet the title "Hitler's Table Talk" is a direct English translation of Picker's title, not Genoud's, and Trevor-Roper's preface claims the translation was made from the German original of Martin Bormann. Genoud's version ends in 1942 (his preface declares an intent to publish the rest in a second volume, which never transpired), as does Picker's (who did not have any material beyond 1942), while Trevor-Roper and Jochmann continue with entries up to 1944.

Assuming any published text is a genuine copy of these notes, Picker's edition (especially where it agrees with Jochmann) carries the strongest claim to authenticity.

It contains the actual German, and was the first to be published, a year before Genoud, and though Genoud procured a lengthy but essentially trivial preface from Robert d'Harcourt of the Academie Française, Picker had the involvement and auspices of a major university and Hitler historian: "Arranged on behalf of the German Institute for the History of National Socialism, initiated and published by Gerhard Ritter, professor of history at the University of Freiburg."

Moreover, Picker was one of the actual stenographers (from 21 March 1942 to 2 August 1942), and thus transcribed many of the notes himself in the very presence of Hitler, making him an eyewitness with access to the notebooks of his predecessor Heim, which he says he acquired directly, bypassing the editing of Bormann.

Picker's second and third editions also contain several testimonials to the text's accuracy and authenticity by fellow bunker officers, including Gerhard Engel, and also a testimonial by historian Walter Mediger who checked the first edition against Picker's own transcripts and "made corrections" accordingly, testifying to the accuracy of the new edition in relation to those notes. Picker asserted in his first edition that [translating Picker's German] "a sufficient number of the staff at the FHQ lives to be able to testify to the authenticity of the recordings of the table discussions, since Hitler spoke rarely at table on military affairs," and to demonstrate his personal knowledge he gives a detailed description of the bunker and meeting. […]

There may be a clue on the website of the controversial historian David Irving. He relates how Genoud attempted to hoax him in the 1970s with what appeared be a forgery of "Hitler's Last Testament," which Genoud published earlier. Irving even claims he got him to confess to forging this "testament," Genoud declaring in his defense "But it's just what Hitler would have said, isn't it?" Irving's story throws a lot of suspicion on Genoud as a man willing to perpetrate a hoax, thinking it permissible to fabricate the words of Hitler if it was what he believed Hitler "would have said." Such a man would likely have no scruple against altering and insert words and remarks into the Table Talk.

Further study of Genoud's history and motives, and the nature of the distortions he introduced into the record, would be worthwhile. He appears to have been a very strange man with a colorful history: a Swiss banker and Nazi spy who laundered money for the Third Reich, a self-professed neo-Nazi right up to his suicide in 1996 (though never an open supporter of the holocaust), a voracious purchaser and profiteer of Nazi archives, and an admitted financer of terrorists."' But I will leave it to more able historians to explore the facts of his life. Whatever Genoud's motivation for doctoring the text, the fact that Stevens and Cameron's English translation matches Genoud's falsified French (as we shall see), and not the actual Bormann-Vermerke published by Jochmann, leaves many questions unanswered. Were they lazy? Duped? Accomplices in crime? Whatever the case, the Trevor-Roper edition is to be discarded as worthless. […]

It is sufficient to note that, whatever his beliefs were, they are distorted in Genoud, and these distortions among many others were retained in the text of Trevor-Roper. Yet that is the only English translation of the Table Talk in print, and few know how worthless it is.

Hugh Trevor-Roper is known from his involvement as an early expert witness when the Hitler Diaries were published in the early 1980s. People were quite quick to nickname him "Hugh Very-Ropey" afterwards, while many sprung to his side and defended this as on honest, one-time mistake. That it was not. He did it again, of course, and before, many times. One such instance is this Table Talk:

Mikael Nilsson: "Hugh Trevor-Roper and the English Editions of Hitler’s Table Talk and Testament", Journal of Contemporary History 2016, Vol. 51(4) 788–812, 2016
This article examines the publication of the famous ‘Hitler’s Table Talk’ and ‘The Testament of Adolf Hitler’ as well as the role of British historian Hugh Trevor-Roper in this process, including his relationship with the Swiss banker François Genoud – the owner of the ‘original’ manuscripts. The article is based on research utilizing Trevor-Roper’s personal correspondence and papers; material that has never before been used to investigate this matter. Besides shedding light on many previously unknown details concerning the publication of these documents, the article shows how Trevor-Roper consistently failed to enlighten his readers about central source-critical problems connected to the documents he was validating. He did so on numerous occasions and through several editions of the sources, even though his personal correspondence shows that he was well aware of the problems. The article argues that Trevor-Roper chose not to reveal these problems in public so as not to upset his business relationship with Genoud so that he would gain access to further documents in Genoud’s possession.

These findings rule out any reliability at all for the given text overall in English versions. As indicated in the early review, even the German text contains factual errors, impossibilities and a huge lot of lies, seemingly or really from Hitler's mouth.

German historian Peter Longerich concludes in "Hitlers Stellvertreter. Führung der NSDAP und Kontrolle des Staatsapparates durch den Stab Heß und Bormanns Partei-Kanzlei", K.G. Saur: München, 1992, p 6, that the Bormann papers are so unreliable and originals inaccessible, that they have to be viewed with "skepticism". Fact is indiscernible from fiction and without external evidence, not a single word from the book can be trusted. The German original was written, and rewritten by Nazis and revisionists, during the war and after it. All foreign translations were written, rewritten and expanded, sometimes demonstrably doctored, by either revisionist right wingers like Genoud or very greedy and sloppy, if not downright fraudulent historians like Trevor-Roper. Newer editions of varying quality and state of the underlying text are now published by a well known right-wing revisionist publishing house in Germany, not known for having anything reliable on offer, completing the circle.

Conclusion on Table Talk

Since the "Table Talk" and books like that are the source for the quote in the compilation that originated the question, many originals of the sources for that book disappeared, or are not accessible, or were just fabricated, regarding that quote we have to conclude:

• Did he say any of that what's in that book?
  • Maybe? We have no reliable proof in either direction.
• Except, that he almost certainly did not say what appears in the English translation.

The main steps leading into this conundrum:

• Hitler said something.
• the Nazis Heim or Picker wrote some of that partially down the next day, paraphrasing Heim's words: "as best as he was able to capture and recall the gist of it, often failing to do that reliably".
• Hitler and Bormann went over that to approve and redact it.
• Picker and Heim assembled some of the stuff after the war. That material is considered unreliable in principle by leading historians – including the editors of this material.
• Genoud then published the available material in his French translation with his own redaction and added completely fabricated material, claiming the material to be completely truthful…
• The English version translates that last French version and gets endors*m*nt from a systematically sloppy historian.

• That version is then quoted in the book of the claim in question but now even completely out of the context which was already unreliable at the source.

  • What comes closest to what he might have said in 'a' German original is not from steganographic note-taking in the event but stemming from minutes from memory written some time after the fact. That still cannot be read in the overreaching fashion of the English translation in the claim.

Historians must be aware of all this when they use these sources. It is an inevitable conclusion of this essay that historians should refrain from immediately quoting these sources as if they were reproducing Hitler's words verbatim - this is simply not the case. The table speeches were written with the express purpose of conveying the illusion that one could meet Hitler face to face, that is, they were created over long distances to create confusion and deceive.
_{–– Mikael Nilsson: "Hitler redivivus. „Hitlers Tischgespräche“ und „Monologe im Führerhauptquartier“ – eine kritische Untersuchung", VfZ 67 (2019). DOI 10.1515/vfzg-2019-0004}

Example 2: Speer's "memoirs"

Since his imprisonment in Nuremberg and Spandau, Speer has worked to stabilize his somewhat positive image as an apolitical technocrat and misguided idealist through extensive secret written records (which were smuggled outside to his friend Rudolf Wolters in Coesfeld with the help of a nurse) by the Nuremberg Trial, while concealing all the negative points of his biography (promotion of the concentration camp expansion, expulsion of Jews from Berlin). Particularly in his two very successful book publications, Erinnerungen von 1969 and Spandauer Tagebücher von 1975, he reverses decisive phases of his activities in the "Third Reich" to some extent.

The Speer biography of historian Magnus Brechtken, published in 2017, confirms Schwendemann's assessment by means of a confrontation of Speer's narratives with the sources. Speer's memoirs with a world circulation of almost three million copies, as a seemingly authentic contemporary witness report, had shaped the historical picture of a small group of criminals around Hitler who were responsible for war, the Holocaust and slave labor, while Speer wanted nothing to know about it.

The Spandauer diaries, in which Speer describes the years of his captivity and at the same time recalls his time in the closest NS leadership circle, served the same purpose, describing and ridiculing the characteristics of his fellow prisoners (Baldur von Schirach, Rudolf Heß, Karl Dönitz, Erich Raeder, Konstantin von Neurath, Walther Funk). The legend that he had the New Reich Chancellery built in less than twelve months is also repeated in both books (and thus a legend devised by Nazi propaganda to underpin the alleged efficiency of the Nazi system) Spear biographer Magnus Brechtken describes the diaries presented in Speer's preface as allegedly authentic as "literary invention" in the light of the sources.

Brechtken considers the widespread legend that Speer ignored Hitler's final orders to destroy infrastructures in Germany to be particularly spectacular, thus making the later economic miracle possible. Particularly striking is the episode in Speer's "Memories" that he allegedly confessed Hitler's refusal to obey orders shortly before the end of the war in the Führer bunker and left him with tears in his eyes, because this scene was invented by a French journalist in 1952. Speer found it useful and therefore made it his own in the book.

Joachim Fest (1926-2006), who as an editorial consultant had played a decisive role in Speer's publications and thus in his self-stylisation, later stated that Speer had "turned our noses with the most trustworthy expression in the world"

"Speer is a prototype for the social group of the functional elites who consciously chose Hitler and gave National Socialism its actual dynamism through their expertise. Without all the doctors, lawyers and administrative experts, the rule could not have functioned so well. Speer was basically only one of the most committed, ambitious and hard-working. That's why after 1945 he was also the ideal figure for all those who wanted to say: "I did participate, but I didn't hear anything about the crimes". Even people who marched along at the front were allegedly not involved afterwards. Speer, like everyone else, knew exactly what he had done. He very successfully denied and repressed that afterwards."
- Magnus Brechtken
_{–– Wikipedia: Albert Speer}

Example 3: Private secretary Traudl Junge

It is in large part her account that formed the basis for the movie Downfall.

It is worthwhile to examine this quotation more closely. Junge does not exercise self-criticism here, but a normative one. In her opinion, what she tells has actually happened in this way, but it does not fit into her current view of history. The terrible Hitler cannot and should not be the same one who lovingly trains his bitch. The conflict between what Junge can remember and what she wants to remember pervades her entire autobiographical conversation.

The thoughtless reproduction of the intimate and allegedly authentic stories about Hitler are not only a media-cultural problem, […]

Traudl Junge was by no means a victim of history, but the price for her successful integration into post-war society was the tabooing of part of her memories, because these memories had already arisen at the time of their creation under the conditions of a narrowed and distorted perspective and had become problematic in the Federal Republic since the 1960s at the latest.

_{–– Benedikt Tondera: "Die gespaltene Erinnerung Traudl Junges. Eine Analyse der autobiographischen Erzählungen Traudl Junges und deren medialer Inszenierung", BIOS Zeitschrift für Biographieforschung, Oral History und Lebensverlaufsanalysen, Vol 21, No 2, 2008.}

Our post-fascistic fantasy

It was in the spring of 1932, in the midst of presidential elections, that the National Socialists discovered the publicity value of Hitler’s private life. […] Having proved its broad appeal, the image of the private Führer would become a staple of National Socialist propaganda for years to come.

The coming out of the Führer’s personal life marked a distinct departure from earlier National Socialist publicity, which had focused on Hitler’s role as agitator of the masses and leader of a militant political movement. In the 1932 runoff election, the need to cast a wider net pushed Nazi Party propaganda toward a celebration of the personal attributes of their candidate. […]

Perhaps most daringly, Nazi publicists brought Hitler’s private life into the limelight in order to emphasize his moral and human character and thereby win over the bourgeois voters and women who had overwhelmingly supported Hindenburg on the first ballot.

Given the circumstances of Hitler’s private life, this was truly an audacious move. […] While the Nazis continued to fight reports that could harm Hitler’s reputation, they began to construct for public consumption their own version of the private individual. The image of “Hitler as private man” would now be reconfigured into an asset rather than a liability.

The title of Heinrich Hoffmann’s photo album, The Hitler Nobody Knows (Hitler wie ihn keiner kennt, 1932), announced the shift in the Führer’s image. The book appeared in mid-March, shortly after the first presidential election. While conceived earlier and perhaps independently, it nonetheless served as an effective tool in the National Socialists’ new campaign to appeal to a broader public through the recently discovered “private Hitler.”

Hoffmann, as Hitler’s official photographer, had extensive access to the German leader, and from the thousands of images at his disposal, he selected one hundred to encapsulate the Führer’s personal life.

[…] In fact, and as Germans were to learn after the war, Hoffmann’s distorted and highly edited vision of Hitler’s personal life bore little resemblance to reality; Eva Braun, for example, would be banished from such portrayals during the Third Reich, despite becoming a fixture of his inner circle by 1936.

The dust jacket text further suggested that the book would serve as a visual complement to Hitler’s Mein Kampf, and the book did begin biographically, like a family album, with photographs of Hitler as a baby (with a birth announcement “pasted” in the corner), the house where he was born, his parents, his school and army days, and his rise as an orator and politician. In documenting Hitler’s contemporary life, Hoffmann included an assortment of photographs that mostly appeared to be candid shots of Hitler engaged in activities either of a private nature or at the peripheries of his political duties—for example, stopping for a quick picnic lunch on the way to give a speech or chatting with a worker who approached his car. Relatively few of the images revealed an urban landscape; instead, Hitler’s so-called private life played out mostly on a pastoral stage. A number of the images of Hitler at leisure focused on the Obersalzberg, although Haus Wachenfeld, while described, was not visually depicted. Hitler was shown in the mountains with his dogs, reading outdoors, walking, talking with a neighbor’s child, and dressed in casual clothes, including lederhosen. Here, a caption stated, away from the “noise and restlessness of the cities,” Hitler could relax and recover from the “stresses and strains” of his political struggle. Yet despite the pretext of being personal, these images of a relaxed and often smiling Hitler were by no means apolitical. Thus, a photograph of Hitler sitting in the grass reading the newspaper and grinning broadly was accompanied by a caption indicating that he was amused by the “fables” printed about him by a hostile press: “champagne feasts, Jewish girlfriends, a luxury villa, French money …”6 The viewer, at whom Hitler gazes, is invited to share in this intimate moment and laugh along with him.

On a deeper level, the book as a whole served a political purpose: to recast Hitler, through the vehicle of his private life, as a “good” man.

_{–– Despina Stratigakos: "Hitler at Home", Yale University Press: New Haven, London, 2015.}