You're essentially saying that our brains can't exist.

But they do, and we can copy them, what is the problem with making a synthetic brain? Why is the natural brain an allowed exception, but the one we make is not allowed?

Edit:

On the one hand you want to use Church-Turing to invalidate the possibility of us creating non-Turing based technology, and yet in a previous post you claimed the human brain likely violates Church-Turing. So which is it? Is reality allowed to violate Church-Turing or is it not?

If you honestly believe that the human brain violates Church-Turing, then you have to explain why you also believe that we can not copy the brain and achieve the same result ourselves.

If the universe is not computable, and if the non-computable aspects are relevant to the functioning of the human brain, then our ability to build a brain simulation is strongly limited. A functioning synthetic brain would have to leverage the same relevant natural phenomenon as a real brain; a mathematical simulation running on a standard computer would not suffice.

I do think that I actually agree with your earlier point that once we have a functioning synthetic brain, we can ignore subjective experience itself and just focus on its functional implications for the entire system.