In your opinion what causes christians to believe in Jesus

[John 6IX Breezy]

Different areas of the brain may have different functions relative to each other, but they are all achieved through the same physical mechanisms, which follow the laws of physics and thus, barring quantum effects, are determined in my view, and thus cannot be considered 'free'.

I think you should explore this point further, because what matters isn't whether neurons obey physics (they do), but whether free will can emerge from the system as a whole. And you’ve already opened the door to this possibility by noting that the same neuron can contribute to vastly different functions. If one set of neurons allow you to see the world, and another set allows you to give a lecture, and still another allows you to do a backflip, then we're dealing with a wide, if not unlimited, palette of functions that can emerge from simple neurons obeying physics. And one such function, I would argue, is the ability to make choices.

Another aspect to consider is that free will seems inseparable, at least in humans, from consciousness itself. One only makes sense in the presence of the other. And consciousness doesn't seem to play nice with reductionist views. So, in my opinion you’d need to account for consciousness before you can dismiss free will.