I think the issue is the word simulation. What is a simulation?

It implies that the thing doesn’t really exist, but how can something not exist?

Let’s say the computer game Frogger is a simulation. The electrons in the computer are very much moving in reality. The bits are changing and following the rules of the code. How is that not real? Okay, so we know it’s not actually a frog, but the electronics are working just fine physically and creating the pixels so we can see what is happening. It is happening even if it’s only a simple “universe” of dots on a screen.

So, let’s say that something is a simulation when someone uses a system to test algorithms. If the universe is such an experiment, then it’s still as real as ever because the algorithms are actually carried out. Atoms are moving. It is real, even if it’s a simulation.

Like all other kinds of thoughts about who created the universe, what was before big bang or what happens when we move in the fourth spatial dimension, it’s all just speculation. There’s no proof of any of it being possible or existing, because it’s based on something being “outside” the universe.

Similarly, asking for concrete proof of the simulation theory not being fiction is a logical fallacy. It can only be up to the believers to prove it.