1. There is a huge difference between sentience and intelligence. If something kills me I don’t care if was sentient if it was smart enough.
2. Saying that we don’t understand something because "quantum" makes no sense. Actually, modern computers work on quantum effects.
3. I am not aware of a scientific argument that anything physical (like a brain) cannot be simulated by a computer.
That being said, it might still be super hard and long of, so I am also sceptical of the hype.