By your parenthetical I assume you know of chaotic systems. But yeah, its been some time since I read philosophy but I vaguely remember that you still aren't guaranteed free will just cause things are undeterministic. This is because since you cannot show that an event was caused you cannot prove that your actions led to the event. How do you know that it is because of your actions that some event occurred or you chose to act as you did if things don't necessarily lead from one another? And the other side is true too. Just cause things are determined does not necessitate free will be lost. It was usually sugar coated but I always took it as even with just the illusion of free choice, that ability to be able to seemingly choose what you would have anyways is free will.

I stopped thinking about such things as I always got stuck in a head wrenching recursive loop of futility.