Also the hard deterministic view of the universe gets incomplete at the quantum level, so maybe our brains do have some spark of pure chaos that gives us non-deterministic freedom.
Consider thermodynamics: even without quantum weirdness, we can't compute/predict the micro interactions of atoms in a gas. But most average out, and we can make a lot of meaningful predictions on a macro scale.
Back to brains: even if there is some underlying quantum process that might free us from full determinism, on a macro level, it might not matter - you're still gonna value what you value, and make the same "choices".
And if in some cases a "decision" is actually impacted by some quantum effect... is it "agency"? Or just yet another external process affecting us?