My high school physics teacher once said that, if we ever find something that is outside the universe, then we will obviously be smart enough to call that the universe also. Because "universe" is a definition that means "everything".
Similarly, if we ever find a reality beyond reality, we'll just call it reality. Because that's how it's defined. It means "everything".
Or put another way: Of course we live in a simulation. Your experience of the world is just an emergent property of how your senses and neural system interact. There's no real reality. You're already trapped in a dark box doing fly-by-instruments using signals processing to interpret what your nervous system is detecting.
Is that not already a simulation anyway? Maybe not. Maybe it depends on how you define "you".
Fundamentally, would knowing that you're in a simulation change anything?