Yes reality is non deterministic but we don’t know if you absolutely need to consider anything outside the immediate closed system for a reasonably close approximation given the same inputs. They can already repeatably (inexact of course) simulate muscular actions with the same stimuli like from Neuralink. Exact enough to let a paralyzed person draw with their mind.

Yeah the last line is a cheap shot, possibly at myself.

Yeah, I think it would be an interesting thought experiment to replace parts of a brain with Neuralink-like devices until you have a fully digital brain, although I doubt it would end up anything like a current LLM.