Simulation theory makes no inherent moral prescriptions or assertions about the ultimate origin of the universe - it just rolls everything up a level - This universe is a simulation inside the real universe... What created thecreal universe? We're not trying to answer that.

Theism tends to make moral prescriptions and point to an immutable god - This universe was created by God... What created god? It's god, dude.

This is why simulation theory and theism are compatible - there's no reason both can't be true - though we can never know if either is true, so just get on with your life and try to be a decent human.