Do you control what you believe?

[Angrboda]

On the other hand if the scientifically indeterministic - in the sense that it is unpredictable - quantum world is nevertheless philosophically deterministic, then everything is still ultimately entirely determined so in what sense do we ever "force" anything if "we" are ultimately entirely forced by the causal chain back to the big-bang that precedes us?

The half-life of uranium-238 4.468 billion years. This means that in ANY sample of uranium-238, at the end of 4.468 billion years, one half of the sample will have decayed. This is a clockwork system of precision. There are other radioactive materials and they all have the same properties albeit different half-lives. Fully, precisely, predictable. But we have not a clue one which atom is next or why. Absolutely, completely unpredictable. If they do one day figure it out, then the last vestige of hope for any free will or indeterminate universe flushes down the drain.

This type of predictability would require the demonstration of what is known as a hidden variable theory (of quantum mechanics). There was a communication in the last year in Nature Communications, IIRC, that claimed to demonstrate that no hidden variable theory could yield better predictive ability than the current interpretation and framework. If that result is robust, it would seem to indicate that such hidden variable theories cannot improve on our ability to predict the results of radioactive decay, which is basically zero predictability.

If I accept your argument as-is, it would seem you are suggesting that such predictive ability would preclude any free will. (I sense Heisenberg's ghost in the room.) However, I would note that this seems to be an argument from ignorance. As such, I couldn't at this point accept your conclusion. Perhaps, just as with theism and atheism, there is a tendency to want to try to prove the negative that there is no such thing as free will, when, perhaps it would be more prudent to dispense with specific individual claims made by proponents of the existence of free will.