Appreciate the thoughtful comment. Yes, under the hood indeed "every physical system is quantum", yet at the macro level physical systems are more or less predictable, including the brain. The brain's immensely complex structure and extensive interactivity make understanding how it works largely a mystery. The relatively simplistic models we're able to create have so far illuminate only a small part of its functionality.

The idea of free will has been a subject of eternal debate. I suspect this reflects lack of consistent definition. I would posit that free will isn't absolute but necessarily constrained by the nature of individual exercising its will. The stochastic attributes of a system or entity mean its actions are to an extent unpredictable, providing an "opening" for willful behavior.

Humans imagine they have free will because they're aware of their decisions or actions while unaware of the range of factors contributing to a decision or action. Intuitive (vs. analytical) cognition is the operational default. By definition intuition is a computation occurring outside of the person's awareness.[0] Consequently, it augments the impression of exercising unfettered free will.

Perhaps it's most accurate to say we have will or volition but not free of constraints imposed by our biology and physical/social environments. While the randomness inherent in biological systems allows volition to evolve, it also limits what an organism can will itself to do.

[0] Journal of Cognitive Engineering and Decision Making 2017, Volume 11, Number 1, March 2017, pp. 5–22