ok so
determinism is (not) the idea that you can perfectly predict the future by knowing the position and momentum of every particle
which makes sense because obviously you can calculate where a particle is going to go and what it will do for every particle etc.
this also means there's technically no free will because your brain is also particles and stuff
but your personality is based on that so there functionally is free will
however
quantum randomness is "true" randomness, meaning that sometimes, things can just happen which cannot be predicted by knowing the position and momentum of every particle: new particles can randomly come into being
so now you can't predict anything, and determinism is invalidated
however
that still means there's no free will, because that's just random changes to the model and not conscious decisions to change it
however
assuming time is self-consistent, meaning time loops both can exist and don't result in paradoxes, free will actually does exist. this is how:
in Macbeth, the witches make a prophecy. a prophecy at its core is information from the future/sent back in time; just accept that definition for now. the fact that macbeth will become king is sent back in time from a point where he is. Lady macbeth, hearing about this, orchestrates events that cause macbeth to become king. this is a stable time loop.
this stable time loop hinges on lady macbeth's actions in the situation where information comes from the future. her actions there aren't exclusively determined by the previous state of her brain and her world, because something that violates causality occurred, meaning her next actions are based on the position and momentum of all particles, and an outside influence. basically, lady macbeth's personality decides what she does in a new situation. which is exactly what the common understanding of "free will" is.
likewise, in Homestuck, the character Vriska Serket decides to bring about the existence of the antagonist because she already knows that the antagonist will be brought into existence. she decides that, since his existence is inevitable (due to being in the future, which she knows), she should have a hand in it, just to be cool.
obviously this is a stable time loop: vriska created the antagonist, and because she did that, she decided to do that
lady macbeth orchestrating those murders and vriska orchestrating the creation of the antagonist that functionally the same thing: someone's personality directly affects the creation of a stable time loop, independent of standard determinism. they actively make a choice which is not determined.
in Ted Chiang's 2007 novelette The Merchant and the Alchemist's Gate, the main character, a fabric merchant, meets a man with a portal to the future. the merchant says "say someone saw themselves alive in the future. would they not then be able to live dangerously, knowing that they would not die?"
the man responds, "a person willing to live so dangerously would not see themself alive in the future"
and, yeah, that wouldn't be a stable time loop. that is a clear example where a stable time loop either does or does not exist based on someone's personality, not their actions
your personality determining your actions is what free will is
ergo, in a universe where there can be stable time loops, (i.e. a self consistent one with time travel), there is free will