Does modern scholarship accept an Ethiopian or Nubian origin for Egyptian hieroglyphs?

The Nile Valley civilization, even according to the suspect dating of western academia, spanned at least 3000 before the invasion of Alexander of Macedonia in 332 B.C.E.

Geographically, the distance between current day Egypt and Ethiopia is a relatively short distance of roughly 1300 miles.

The origin of the Ancient Egyptian so-called "hieroglyphics", or MDW NTR, are sacred symbols which have not been "deciphered", "transliterated", or "translated" to english, contrary to the claims of Young and Champollion; and their modern day adherents, that is those who supposedly study "egyptology". Any individual who claims to have the ability to "transliterate" symbols to english letters and words immediately suspect of outright lying. There is no way for them to confirm their own interpretation of hieroglyphics to english words. For example, there is no clear and universal definition for the english word "race". Multiple disciplines within western academia have dismissed that "race" has anything to do with biology or genetics, however, at least in the U.S., "race" is used by the state for political classification schemes. Works attributed to "Manetho" are frauds. Similarly, many have no clue what hip-hop artists are talking about, unless they are familiar with the culture; even then E-40, Mac Dre (R.I.P.), Black Thought, Mobb Deep, Suga Free, Kendrick Lamar, etc. constantly develop new words and meanings for "english" words that are not found in any dictionary. An individual would need to ask what the words mean or be intimately familiar with the culture to, potentially, understand what the words mean. It is impossible to convert a symbol to a letter or word without asking the individual who wrote the symbols in stone or in papyrus what the symbol means. No individual who claims to have the ability to "transliterate" or "decipher" MDW NTR have ever asked any African Ancient Egyptians what those words mean.

The word Ethiopian in Greek is derived from the word Aethiops, meaning Of the burnt face. It was a generic term for black skinned people similar to latin words like Niger, Hebrew words like Kush, spanish words like Moreno or Moor.

I am aware that there are some black skinned peoples who are native to Southern Egypt. They still live there even till this day; The Nubians. He may have been referring to them or so it seems.

What is the position of modern scholarship on these claims?

The so-called "Greeks" are, at best, only secondary sources for any African culture or state; they are foreign invaders, not indigenous peoples of any part of Africa. By the way, Ancient Egypt is in Africa, not some fictitious military concept such as "Middle East", "Near East", etc.

It is not clear what the term "black skinned peoples" was intended to mean in the minds of the foreign invaders "Greeks". Ask them what they mean. The "black skinned people" the Minoans? Or any other "black skinned people" found in antiquity around this entire planet - before there was a notion of a non-"dark skinned people" - as no one else but "dark skinned people" existed on this planet, Earth. It is not physically possible to derive "black skinned people" from "mauve skinned people" or "pink skinned people" or "white skinned people". "black skinned people" are the original people on this planet, from which all other "__ skinned people" are directly derived from (without going into Neanderthal and Denisovan DNA found in Europe; the original Autraslian peoples, etc.). Thus it should not be a shock that "black skinned people", that is, the Ancient Egyptians are the first literate people on this planet.

Ancient African culture is not based on some arbitrary "skin" concept. "skin" fetish, obsession and history revisionism is the mind of people who view "black skinned people" as foreign to them, not as their parents, the origin of modern human beings, and humankind. Or, that somehow, the Ancient African Egyptians were not both "black skinned people", what ever that is supposed to mean, and "brown skinned people"; thought what they were not is "mauve skinned people" or "pink skinned people". The African Ancient Egyptian ancestors at least left no doubt in the architecture which survives today what "skin" "color" they are. For that reason, people have to try to claim Ancient Egypt from the the outside looking in - after antiquity ended, circa 332 B.C.E., from a foreign "Greek" perspective, who had nothing at all whatsoever to do with the origin of the African Ancient Egyptian hieroglyphics, as their is little if any primary source evidence that survives which demonstrates so-called "Greeks" were literate prior to their contact with the Ancient Egyptians in actual history, not mythology.

Returning to what you have termed "modern scholarship", you can find whatever you want given a predisposed notion of what you expect to find. From the perspective of African culture, the Nile Valley civilization is a single culture, spanning the breadth and length of the Nile river, further up south into Ethiopia's highlands, over 1000 feet above down north. Rivers are a highway for languages, foodstuffs, inventions, etc. The Ancient African Egyptians are the smartest people in the world during antiquity, as evidenced by the tens of millions of actual artifacts which survive from before the concept of Europe and "Near East", "Middle East", etc.

So, read the "modern scholarship" of "dark skinned people" and "brown skinned people" relevant to the Nile Valley civilization - even if you do not like or agree with what they are stating - to get a better sense of the culture African Ancient Egyptians, as those are the direct physical descendants of the African Ancient Egyptians, not foreign invaders peeking in from afar leaving their opinions for history to try to give greater weight than at best secondary source, visitor, student, military invader. A distant visitor or military invader can never compose an accurate account of thousands of years of history which occurred before their invasion or visit. Similarly, one cannot ask Greeks or Europeans or English or German or French or "Middle East" or "Near East" people what the meaning of the sacred symbols of Ancient Egypt in Africa are; none of them were there when the symbols were being carved into to stone to ask what they meant then; they can only guess, and at worst, simply lie, about the origin and meanings of the hieroglyphics of Ancient Egypt in Africa.

The earliest evidence for Egyptian writing as writing (used to record language) goes back to circa 3250 BC, in the city of Abydos. Traces of earlier symbol use in an accounting context (e.g., cylinder seals) have also been found going back to about 3800 BC, indicating a gradual transformation of symbolic markings into an actual writing system. See here for a recent summary.

So it's pretty clear that the Egyptian writing system was developed in Egypt; some scholars argue that it may have been inspired by the slightly earlier example of Sumerian cuneiform (or the accounting-symbol precursors of cuneiform).

As far as I can tell, the earliest evidence for writing in Kush (the usual name for the ancient kingdom immediately south of Egypt and plausibly what the ancient Greeks meant by "Ethiopia") is the use of recognizably Egyptian hieroglyphics and demotic in the Napatan period (circa 800-590 BC), possibly as a result of Egypt's conquest and occupation of Kush in the preceding centuries (from the 16th C BC down to the disintegration of the Egyptian New Kingdom around 1070 BC, after which Kush became independent again). Later, the Meroitic script emerged, sometime prior to the 2nd C BC, when the first known Meroitic inscriptions were made.

You should keep in mind that Diodorus Siculus visited Egypt in the 1st Century BC as a tourist, more or less. There's no evidence he learned Egyptian, let alone that he learned to read Egyptian (hieroglyphic or demotic) and then tried reading any ancient inscriptions. He's also notorious for apparently not having bothered to use the work of Manetho, a fairly authoritative history written (in Greek) by an actual Egyptian about two centuries earlier.

A wild speculation: in the 740s BC, the ruler of Kush was able to conquer most of Egypt, establishing what's known as the 25th dynasty, which ruled Egypt until the Neo-Assyrian Empire invaded circa 670 BC. It is perhaps possible that what Diodorus Siculus is relating is based on a garbled memory of the Kushite conquest and the 25th dynasty.

The short answer is no. Although the origins of hieroglyphic writing are disputed to some extent, modern scholarship leans towards the idea that it developed independently in Egypt, but "no definitive determination has been made as to the origin of hieroglyphics in ancient Egypt".

In Middle Egyptian: An Introduction to the Language and Culture of Hieroglyphs (2014), James P. Allen states:

Unlike Mesopotamian cuneiform or Chinese, whose beginnings can be traced over several hundred years, hieroglyphic writing seems to appear in Egypt suddenly, shortly before 3200 BC, as a complete system. Scholars are divided in their opinions about its origins. Some suggest that the earlier, developmental stages of hieroglyphic were written on perishable materials, such as wood, and simply have not survived. Others argue that the system could have been invented all at once by an unknown genius. Although it was once thought that the idea of writing came to Egypt from Mesopotamia, recent discoveries indicate that writing arose first in Egypt.

Toby Wilkinson, in The Rise and fall of Ancient Egypt (2011) supports this view:

Hieroglyphs are so perfectly suited to the ancient Egyptian language, and the individual signs so obviously reflected the Egyptians particular environment, that they must represent an indigenous development.

Wikipedia cites Geoffrey Sampson in Writing Systems: A Linguistic Introduction as favouring a possible Mesopotamian influence, saying that

came into existence a little after Sumerian script, and, probably [were], invented under the influence of the latter

Sampson adds that it is

probable that the general idea of expressing words of a language in writing was brought to Egypt from Sumerian Mesopotamia

but concedes that

no definitive determination has been made as to the origin of hieroglyphics in ancient Egypt....a very credible argument can also be made for the independent development of writing in Egypt...

In The Hieroglyphs of Ancient Egypt (2001), Aidan Dodson concurs, stating

No one can be certain what stimulated the development of this early script.

and adds that the idea of writing may have come from Mesopotamia, though he emphasizes the differences between the two writing systems.

No one is talking about Ethiopia or Nubians, though, and Diodorus is not the most reliable of sources on Egypt even though he spent some time there (although we should certainly be grateful for the works of his which have survived). As Pieter Geerkens points out in his comment, the Ptolemaic Egypt that Diodorus knew was quite different from the Old and Middle (and New) Kingdoms and this may have affected his understanding of the past.

CONCERNING THE EDITED QUESTION

One can only reiterate that "no definitive determination has been made as to the origin of hieroglyphics in ancient Egypt". Trying to pin down the origin of this script to a precise geographic location such as Ta Seti simply isn't possible and (as Quuxplusone's comment points out) modern borders have little meaning. Also, one cannot assume that the place at which the earliest hieroglyphs have been found is the place where they originate from. Much evidence has been destroyed / lost over time, some of which may (or indeed may not predate) the current earliest evidence we have. We just don't know, and more evidence may yet be uncovered.

On this last point, of interest is this joint Yale and Royal Museums of Art and History (Brussels) expedition. This report (2017) mentions hieroglyphs "in the northern desert hinterland of Elkab" in Upper Egypt dating back to 3250 BC. Even earlier (4000 to 3500 BC) is some rock art which, according to Yale professor John Coleman Darnell

preserves some of the earliest — and largest — signs from the formative stages of the hieroglyphic script and provides evidence for how the ancient Egyptians invented their unique writing system

A more detailed survey on the origins of the earliest hieroglyphs can be found in sempaiscuba's excellent answer to his own question: Were the earliest Egyptian hieroglyphs ever discovered really found in Qustul in Ancient Nubia?