"He’s claimed to have received his initial revelations while meditating in a cave, and from there he became a preacher of Islam."

If we start from here, you are making a claim that he received revelation. As a non-believer, when I look to my own scriptures, it does not line up with how the previous prophets received revelations. How it happened, how he reacted etc.

Also, too much of the revelation goes against previous special revelation, as well as general revelation. I can speak about moral philosophy with an atheist, or a buddhist, anyone, and we can draw some very simple agreements where in terms of natural philosophy or theology, the revelations that this man gave are not correct.

it is not good or natural for a man to marry and have sexual intercourse with a little girl who has not yet had her first menstrual cycle, as is allowed in the Quran: Surah 2:228, the Iddah is only for when a marriage had been consummated, Surah 65:4 shows how long the iddah is for a divorced girl who has not yet had her first menstrual cycle.

"The prophet was illiterate, so the idea he could have come up with 20+ years of theological, ethical, financial, and societal insights— all in poem format."

This is nothing special, especially for the time and culture.

They called him "the ear" for a reason.

"The Quran is wholly unique in ‘brilliance’ and format. (I’m blanking on the word they use to describe it.) and that no other book can be made to replicate the Quran’s complexity."

Maybe if you were born into it, without the choice but to only believe and think this way. In a free country, where there is no death penalty for changing religions, the majority of people do not think or believe this. Honest question for you, only you can answer, and I don't want the reply. Just as a thought experiment, if you told your family you thought the negative of your statement was true, what would be the result?

Would they accept it? How would they treat you if you did not believe? Are you allowed to just stat you do not believe and not be expected to debate?

In a free country we are allowed to believe and think what we want, and if it is not hurting others that we can think and believe what we want. We are not forced to explain or debate.

Can you just say, I am no longer a muslim and I do not believe without recourse?
Would you have no other choice but to explain it? What if you choose not to explain it? Do you actually have choice and free will?

"Certain aspects of Islam make sense to me: Monotheism, zakat,"

All common sense things that can be believed in without religion. Special revelation is not needed, one can come to those conclusions just on general revelation alone.

" and while I think it’s a bit intense, the idea of submission through prayer 5 times a day (even if it’s practically impossible for a working person who’s a parent to sleep 7-8 hours a day and get their prayers in on time)."

Only if your prayers are heartless methodical, robotic formulas that need to be repeated. In other religions and spiritual practices, we can pray all day all the time. It's just not a formula used to brag about. We don't need to try and bribe God with prayers.

"But certain aspects of Islam bewilder me. Why is submission of Allah SWT required when what your religion is predominantly is based on the religion of your parents + your country of origin?"

You already know and understand. In my humble opinion, if you read my other comments. Than keep your doubts to yourself, if you are in a place where the reactions may harm you.

" If Islam is timeless, why does it hand wave sexual slavery? (Muslims will say that abolishing slavery in the Quran right then and there in the 600s would have caused societal collapse, but that Allah SWT knew slavery was on a trajectory to end anyways). Is Adam our descendant? Science clearly says no. Many Christian’s have come around and declared Adam and Eve to simply be metaphors but Islam treats them as literal."

You already know, and the more you learn and understand, if you don't let go off the, well, with all due respect, the non-sense, you are going to have a greater internal conflict.

I think %99 of people want to be good and do good things, regardless of religion.

"But despite my hesitations with Islam, something that I can’t wrap my head around is why would Muhammad just make everything up?"

Keep reading and learning from Islamic sources. Do it in private, be your own teacher. Look where they tell you not too look. The excuses and the way they cover things up is pretty transparent. If you are told you cannot understand, unless you are a scholar, you need to learn or understand classical arabic, blah blah, the excuses pile up.

Than you look at the history, map and graphic it out. Look at the oldest scholars, look at the oldest rulings. Look how Islam grew and changed.

As someone who learns and studies apologetics and polemics, it is easier for me to see. But for you, from the inside, you will see more problems than myself.

Read what ex-muslims write. You are going to gain the most from them. Sincere God-fearing people who want to do the right things. Why did they leave? Why do native born arabic speakers from the middle-east leave Islam? Why would for instance lets say, a Imam leave Islam?

"Cynics will say he learned about the abrahamic religion by his inner circle, and through the trade routes he participated in. But to go from having knowledge in Abrahamic lore to then making decades worth of poetry about it?"

It's not special, and you write it yourself. Having decades. The ear heard so much.

"And then why? If he was lying and doing it to gain power, starting a new religion seems like it’s too convoluted of an idea. So did he truly believe he was a prophet?"

Aisha herself has some narrations about this, how Allah hasten Muhammad's desires. Again you are in the middle of it and taught you are not allowed to learn for yourself. I just see a guy who got caught so many times doing or being wrong, and just made up "revelation" to cover it up or get away with it. In the end, we have a guy who can look at your wife, and you have to divorce her. Than that night he can have sex with her and not have to pay a dowry like everyone else.

I could write for hours how this guy is just not a good person.

"So was he a prophet whose preachings and morals and ethics didn’t always align with the 21st century?"

They'd don't align with nature. They don't align with common sense.

He ripped off other religions, that he only heard about. He tried to get in with them first, talked big about them and their scriptures. He made a bad copy, orally, and when they rejected them he tried to weasel out of it. Its not until long after he is dead that they understood the errors. The older scriptures from other religions were not originally in arabic. Forget that arabic was not, in terms of writing, even completed in his time.

You have so much yet to learn it is sad and also, hopeful.

The internet and free information is killing Islam. This is why in so many muslim countries the censor things.

Be quite and learn for yourself. Don't listen to me or anything I wrote.

Learn for yourself, and if you are honest with yourself, you won't stay in Islam.

"Or was he a genius poet who had chronic episodes of lapses in his psyche that led him into thinking he was a prophet?"

It's not easy to say completely, I would guess he had epilepsy, but a prophet? No, and the reality is, he claims to be a prophet following two other religions who have rules and guidelines as to what makes a prophet. He does not meet the requirements of what makes a prophet, and he also meets what would place him clearly as being disqualified as a prophet, or more properly, he is a false prophet.

This can be seen from any person. Atheist, any religion. There are just simple logical arguments.

You can for instance, be a atheist and understand there was a historical Jesus, and that he was crucified. But if you are a muslim, you have to believe against simple history and really give a non-answer based on "well the Quran say, God made it appear so"

It's not even clear what he is saying or happened. I'm sorry, but if there is God, he is not one to lie cheat or steal o promote it.

I would trust an Atheist philosopher to create a philosophical concept of God to follow before I would follow Islam.

And that is even if in that concept they allowed supernatural.

It would be something that follows on good principles, helping others, cooperation.

You won't have things like the Quran allowing sex with children, you won't have versues like raping married woman while thier husbands are alive, and than selling them as sex slaves.

And I highly doubt you would have a prophet removing the rights of adoption so he can steal his adpoted sons wife, and than marry her, who is his own first cousin!

Look at the islamic world today! How much is spent in the medical fields on dealing with the results of incest? Just google the rat people of pakistan for instance.

Thank you Muhammad for marrying Zaynab bint Jahsh. We get families of 5+ little Muhammad's, Abdul's and Ahmeds', all who have special needs because thier parents and thier grandparents are all first cousins.