If by “God” you just mean something beyond science: well, there’s always going to be something beyond science until we have a complete theory of the universe, and even then, we may well still be asking, “Why this universe, and not another?”

What would it mean for us to “live in a simulation”? Maybe that down at the Planck scale we’d find a whole civilization that’s setting things up so our universe works the way it does. Well, the Principle of Computational Equivalence says that the processes that go on at the Planck scale—even if they’re just “physics” ones—are going to be computationally equivalent to lots of other ones, including ones in a “civilization”. So for basically the same reason that it makes sense to say “the weather has a mind of its own”, it doesn’t make any sense to imagine our universe as a “simulation”.