There is an interesting thought experiment, I want to tell you about.

Let's assume, we can create human-level AI soon. I mean, it's realistic, right?

Let's further assume, that we want to find out how they are behaving in a closed simulation - add some rules here and there and watch them living a high-speed life like in the game "civilization".

Soon they will develop settlements and then cities on their own. They will grow the knowledge about their universe, our simulation. And someday they will develop simulation technology on their own. Not so unrealistic as well, right?

This event will be proof enough that it can become endless. So another matryoshka can follow.

But the likelihood, that we are the first in a potentially endless chain is next to zero. In that (quite realistic) moment, we will have proof that we ourselves live in a simulation.