I think he suffers from a mental disorder.
Physicist Coel Hellier argues Human brains have to be deterministic (though indeterminism would not give us free will anyhow).
It appears to me that his main argument is that no one can give a mechanistic deterministic account of how free will works.
I say that it would not be free will, if that were possible.
I am particularly baffled that any scientist would make this argument. We cannot give a mechanistic deterministic account of how quantum mechanics works. Bell's theorem shows that is impossible. All physicists know this. So why should anyone expect such an explanation of free will?
Mathematician Gil Kalai is a well-known quantum computer skeptic, and a believer in free will. He has a new paper relating these views, Quantum Computers, Predictability, and Free Will. He denies that quantum supremacy has been achieved.