There are some quantum effects in the brain (for some people, that's a possible source of consciousness). We can simulate quantum effects, but here comes the tricky part: even if our simulation matches the probability, say 70/30 of something happening, what guarantees that our simulation would take the same path as the object being simulated?

We don't have to match the quantum state since the brain still produces an valid output regardless of what each random quantum probability ended up as. And we can include random entropy in a LLM too.

This is just non-determinism. Not only can't your simulation reproduce the exact output, but neither can your brain reproduce its own previous state. This doesn't mean it's a fundamentally different system.