The whole “parallel computations” thing is really largely an oversimplification.

The “multiple universes” thing is the “many worlds theory of quantum mechanics” which is just one philosophical interpretation of statistics.

But also having a system that’s hard to simulate is kinda useless as a benchmark. I once attended a quantum computing talk where the speaker said “I can show you a large quantum system that is impossible to simulate classically” and they held up a rock “This rock is a quantum system that’s too big for us to simulate. It doesn’t do anything useful, but we can’t simulate it!”