[jmcqk6]

This is possibly one way to solve it, but I think there is a simpler way, following causal chains and the laws of thermodynamics.

We clearly have systems that can absorb energy for later use - creating a natural "pause" in the causal chain. Each of these pauses create a possible future that is not yet realized. The longer this energy is held, the larger this possibility space becomes.

Free will becomes that ability to hold the pause with intention, and then select from the different possible futures that have been created.

Determinism does not interfere with this in any way. The causal chains all follow the basic deterministic laws of physics. There is space for choice created by holding energy instead of immediately dissipating it.

No quantum mechanics required at all.