I am not saying that follows from the formal UAT, I'm saying that in general, if we assume that the human brain is simply producing outputs in response to input

I am not saying that follows from the formal UAT, I'm saying that in general, if we assume that the human brain is simply producing outputs in response to inputs, I have no reason to believe that a neural net couldn't be constructed to approximate the same outputs given the same inputs. And specifically, the threshold of "good enough approximation" I chose is effectively just a stronger form of the turing test. AI has arguably already passed a weaker form of the turing test (most people in the world cannot tell the difference between a human-written and an AI-written article, for example).