I was into a choose your own adventure books when I was a kid, there was one in particular that you are told in the beginning that there is a perfect ending but you can't get there by choice. There was no path in the book that got you to that page. You had to just decide to not follow the rules and turn to that page.
The whole idea of a balls hitting each other universe went out the window when we hit the quantum era. We have had to adapt to a reality where matter is somehow a statistical phenomena, and the details are always hidden from us in one way or another. Entanglement is another confusing thing, and its super common - not just some rare phenomena in a lab, it's more of a fact of particle interaction
So our brains are somehow statisical-chemical-electric sugar powered supercomputers that have entangled state. And the brain actually stretches across the body, with various chemistry being produced throughout
In short, nobody has any idea how brains really work, it's way more elaborate than current AI. It's also likely impossible to fully simulate a brain - it would have to BE a brain
There's a separate question about the nature of randomness in the universe, but all we can know is that follows a normal distribution over time. It seems truly random from our point of view. Of course, who's to say if God likes to fudge the numbers a little
From all the discussions I've read about Free Will, I'm convinced the term actually doesn't mean anything at all. What would a world with free will look like? What would a world without free will look like? How would a person with/without it behave? Would there be any tangible difference between them?
As far as I can tell, free will is supposed to be a property of a person, which may or may not have something to do with physics, either everybody has it or nobody has it, and nobody has a definition that would let them measure it (without reducing the question to a disagreement over semantics). I think that whether someone believes in free will is a trick question; you can't believe or disbelieve in a something that isn't even a real concept to begin with.
Sam Harris and Jay Garfield have a great podcast about free will. Saint Augustine came up with the idea of free agency in order to get God off the hook for Eve's fall. Fascinating stuff.
Weirdly, I feel like the best argument to free will comes from Dr. Malcolm (famously acted in a pervy way by Jeff Goldblum) who talked about chaos theory. Complex systems have an underlying order. But also, the reverse of that is true, in that simple systems can lead to complex behaviour. Or to borrow a subreddit term, "never tell me the odds."
Due to quantum mechanics, we know this is not true. There is a level of uncertainty and probability and the smallest level of our universe. The deterministic model of the universe has been put to rest a century ago.