Why does one suffer because of ignorance if ignorance is unintentional?

One suffers because of ignorance through the lack of seeing. The kind of seeing that is needed to traverse ignorance is obscured by an internal map of reality and that view is biased and distorted to suit your conditioned state. That reality is basically made of all of the inaccurate information that has come through your six senses (this part can get extremely detailed - Abhidharma casts some interesting light upon this). One small way I can describe this is to notice the illusion below.

What should have happened is the mind is initially fooled by the illusion but if one chooses to further inspect the image one will see the finer constituents that make up that illusion. However, imagine this illusion as being your view of reality but instead of choosing to inspect and examine it, you just accept its initial appearance (ignorance).

Reality is the same. The only difference with penetrating the illusion above and penetrating into reality is the degree of chronological time it takes.

How is a person supposed to "freely/willingly choose" insight/knowledge if that choice is dependent upon already having some insight/knowledge?

For me, the only dependant part is switching focus - that is the choice. That's all you need, the willingness to want to pick it all apart. The rest just shows itself and often in some quite peculiar ways. Like in the illusion above, the knowledge to see how it works is already there, one just has to apply focus to see it for what it is.

Are the persons choices before choosing insight/knowledge completely at random?

For the most part, I'd say yes. The motivating governors are stored in their alaya consciousness..

What kind of insane reality is this??

If you're referring to a reality beyond concept it's incomprehensible to the finite constructs of the conceptual mind.

The short answer is that the path is not about choices, nor even sankaras [there is no sammāsaṅkhāra], it is about effort to reject ''thinking imbued with sensuality, thinking imbued with ill will, & thinking imbued with harmfulness'' and to follow ''thinking imbued with renunciation, thinking imbued with non-ill will, & thinking imbued with harmlessness '' [and avoiding the confusion by a few puthujjanas of the ''kamma that is neither dark nor bright with neither dark nor bright result, leading to the ending of kamma'' with ''the kamma that is bright with bright result''] by ''Being resolved on renunciation, on freedom from ill-will, on harmlessness: This is called right resolve.'' https://www.accesstoinsight.org/tipitaka/sn/sn45/sn45.008.than.html which leads to ''right samadhi'' instead of wrong samadhi https://www.accesstoinsight.org/tipitaka/mn/mn.019.than.html

But later on the training, those efforts become easier and the path is not even about wishing nor effort. Ideally, the path does not resort on ''exertion'' or wishes, or will, because the path is conditioned too, https://suttacentral.net/an11.2/en/sujato , and once a puthujjana only wants to stop dukkha, the observation that ''thinking imbued with sensuality has arisen in me; and that leads to my own affliction or to the affliction of others or to the affliction of both. It obstructs discernment, promotes vexation, & does not lead to Unbinding.''' kills the bad thoughts automatically. And when the ''body was calm & unaroused'', the ''mind concentrated & single. Quite withdrawn from sensuality, withdrawn from unskillful mental qualities,'' the jhanas occurs naturally, through the joy of being moral and having sama sankappas [or vitakka] : saṅkappas of nekkhamma, saṅkappas of abyāpāda, saṅkappas of avihiṃsā. http://www.buddha-vacana.org/sutta/samyutta/maha/sn45-008.html Puthujjanas fail completely to see that joy springs from morality and renunciation. Puthujjanas also confuse the sama sankappas with compassion and love, because those puthujjanas are stuck between their moronic dichotomy of egotism-selflessness and they create the view that the negation of ''thinking imbued with sensuality, thinking imbued with ill will, & thinking imbued with harmfulness'' is the sankara which leads to ''the kamma that is bright with bright result'' which the sankara of compassion and unconditional love and feeling sad that destitute puthujjanas do not have the means to enjoy themselves. These puthujjanas completely skip the ''intention, aspiration, thought, resolve, of sensual desire''... and thus fails to ''understand the reward of renunciation,'' https://www.accesstoinsight.org/tipitaka/an/an09/an09.041.than.html which is exactly what is needed to get into jhana.

once this is done, there is control over the citta:

**'Monks, endowed with seven things, a monk makes the mind turn according to his wish and turns not by the mind's wish.[1]

What seven?

Herein, monks, a monk is skilled in samadhi, skilled in attaining it, skilled in maintaining it, skilled in emerging from it, skilled in the well-being of it, skilled in the range of it, skilled in applying it.[2]

Verily, monks, endowed with these seven things a monk makes the mind turn according to his wish and turns not by the mind's wish.**

https://obo.genaud.net/a/dhamma-vinaya/bd/an/07_sevens/an07.038.olds.bd.htm#p1

A few puthujjanas are obsessed with the word agency and choices and what they call ''the doer'' when they speculate about atta and anatta, especially the puthujjanas who created their ''dry insight'' doctrine. THose people are obsessed with vibrations and ''lack of agency''. They created 4 paths. Each path is an awakening by what they call ''a cessation'' and the path 4 is nibanna when the ''lack of agency'' becomes manifest. As usual with anything imagined by puthujjanas, it has nothing to do with the dhamma. A sotapanna knows already perfectly this ''lack of agency''.

Words like "freely/willingly choose" and determinism are bad words created by puthujjanas who cling to philosophy, to vitakka+vicara+papanca, be it ''buddhist'' or not, then they create their moronic dichotomies, like ''free will''-determinism and then they mix their dichotomies with morality, only to be left stuck on one side of their dichotomy [they love to polarize their opposite ideas, like ''choosing'' is good and ''not choosing'' is turned into ''suffering''[meaning bearing something], into 'enduring'' something [that is not willed] which means it is bad]. Do not rely on ideas created by puthujjanas to understand the dhamma, until you manage to find a buddha who expresses the dhamma with their words... Most of the ideas of the puhtuhjannas are bad and when the dhamma is expressed with their words, the buddha use their words against them. Like the fire worshipers that the buddha met, mentioned in ''the fire sermon''. THose puhtujjanas worshiped fire, reified fire, idealized it, they created a whole doctrine about the cosmos with the vocabulary of fire. Then the buddha arrives and tell them that fire is bad and the holy life is to destroy this fire. hence nirvana has the putting out of fire.

There were puthujjanas in greece who said that ''everything was water''. If the buddha met them, he would have said ''yeah everything is water, and water is bad and the goal is to dry everything that is wet'' [typically, to dry the flow of asavas].

Why does one suffer because of ignorance if ignorance is unintentional?

Ignorant must arising with intention.

Sutta. Ma. Mū. Sabbāsavasaṃvarasuttaṃ:

when he attends to them, the unarisen fermentation of sensuality arises in him, and the arisen fermentation of sensuality increases; the unarisen fermentation of becoming arises in him, and arisen fermentation of becoming increases; the unarisen fermentation of ignorance arises in him, and the arisen fermentation of ignorance increases. These are the ideas unfit for attention that he attends to.

It makes no sense that a person would knowingly choose to be ignorant of what causes them suffering, yet people suffer for "their" ignorance anyway.

Ignorant is "no noble truth knowledge enough to detach from all clinging aggregates". ignorant is not avoiding. It is foolish, blank of noble truth practicing. See Sutta. Saṃ. Ma.

How is a person supposed to "freely/willingly choose" insight/knowledge if that choice is dependent upon already having some insight/knowledge?

The ordinary people never have any insight/knowledge of anattā before they have chance to practice follow Buddhā.

And the knowledge/insight is just four noble truth, which was adapted to be the dependent origination, five aggregates, etc.

Are the persons choices before choosing insight/knowledge completely at random? Do people not have any freedom or autonomy?

It depend on their level, not random. All experience, past life, friends, job, etc., are effect the practitioner. See netti.

I think this may be another unanswerable question.

Everything can answer by pāli and abhidhamma.

I agree with ChrisW here. Your question implies that you take it personally, while in reality it is an impersonal process. What seems like "you" and "your suffering" (as well as all other sentient beings with their respective experiences) arises from an accumulation and "clumping" of tendencies.

In the beginning these tendencies don't have any awareness, but over time they develop into something that can reflect and think, and once there is thinking, it starts generating all these ideas about how things are, how things should be, with suffering arising when they don't match.

But of course, only when there's thinking, there begin some attempts to analyze the situation, and to solve the problem of things being wrong. So thinking is both the source of the problem as well as the way to finding solution. While the situation before thinking is both ignorance and bliss, the primordial Eden without the conflict between right and wrong.

In the early phases of this evolutionary process, the emerging intelligence does not have any capacity for deliberate action. Think about a young child, can it plan its own destiny and decide where it's going? Then, as the intelligence matures, it grows stable and learns to plan ahead and execute its plans step by step. Of course, before it gets wise it keeps making all kinds of bad judgements and suffers their consequences. Why is that a surprise to you?

I have asked a similar or almost exactly the same question previously on this platform albeit with some Buddism lingua (link).

Please see the excellent answer given by @Mishu 米殊 crowned with her excellent statement " Volition the ability to discern doesn't get hindered by ignorance, although ignorance prevented it from knowing the correct answer immediately.

As Plato said " we are all deprived of truth against our will" but we can seek it following the path directed by the Buddha or if we have a superior capacity following our own reasoning.

I don't know, I'm not sure what your background is -- I think the question would make sense, if you assume that "suffering" is a punishment imposed by God for sinning, i.e. for deliberately breaking (for "deliberately choosing" to break) one of God's commandments when you should have known better -- perhaps you're arguing that if you don't know then you are innocent and therefore shouldn't suffer.

I think a better analogy is something more like cancer, or any other apparent misfortune -- e.g. people suffer and die because they don't know how to cure it -- it isn't a question of whether it's fair (nor of divine punishment), it's a question of whether you've learned the insight and skill, maybe the habits, to undo the cause or to not do it in the first place.

Do people not have any freedom or autonomy?

I think they have a little. There's a sutta -- Chiggala Sutta: The Hole (SN 56.48) -- which suggests that we are fortunate to have been born human and in a time or place, where we can learn the Buddha's Dhamma.

Some people teach not only that the opportunity (to learn to practice) is rare, and nt only that we're fortunate to have access to the Dhamma, but also that it (i.e. the opportunity and the liberating effects) is a reason in itself for us to be happy.

Perhaps that's somewhat debatable though, a matter of perspective. Some people argue against the doctrine of "free will", saying that the physical world just does what it does and continues to do that, and that "people" are just conditioned i.e. that everything they do or think is just conditioned by one thing or another. I think that "free will" probably isn't a Buddhist doctrine -- but other people say (e.g. here) that an "exercise of free will" is "what makes Buddhist practice possible".

It makes no sense that a person would knowingly choose to be ignorant, yet people suffer for "their" ignorance anyway.

The arising of ignorance comes from that mysterious "neutral feeling".

There are three feelings: pleasant, painful, and neutral feeling ... Anything felt physically or mentally as neither pleasurable nor painful. This is neutral feeling.” --MN44

In particular, we have:

The underlying tendency for ignorance underlies neutral feeling.

Consider what happens when we see someone who is neither pleasant or painful. When we see such a person, we have a neutral feeling. Having that neutral feeling, we might say to ourselves, ¨Meh. Don't know and don't care". In this way we choose ignorance.

However we can also see deeper, directly know the person, wish them well and even greet them with a warm-hearted "Hello!". In this way we choose metta and wisdom over ignorance.

If one finds that indifference is a habitual response to neutral feelings, one may consider inquiry with enthusiasm as part of one's practice.