AB,
I do not claim to know for certain how the conscious will of the human soul interacts with the physical brain.
That’s the least of your problems. You also do not know
at all how you’d even define “soul”, how you’d demonstrate its existence even in principle, and how you’d address the huge logical inconsistency it would give you of sitting outside the binary deterministic vs random options.
How such a thing would “interact” with anything is a bit like troubling yourself with how exactly leprechauns make their porridge in the morning.
But I do know for certain that pre determined chains of physical cause and effect can't reproduce the conscious will of human beings, unless that conscious will is just an illusion.
You don’t know that at all, and the only available cogent reasoning suggests that the “free” of “free will” in the sense you attempt it
is illusory. What you meant to say was that you don't
like the answer, which is a very different matter.
So what I put forward is a feasible alternative to the unrealistic assumption that our conscious will is just an illusion.
Two fails there: first, it’s not feasible at all (and nor can it be until you finally manage to address the problems with it outlined above); and second, there’s nothing “unrealistic” about the illusory nature of “genuine” free will, however much it may feel otherwise.
Apart from all that though…