Physics has painted a pretty strong case for multi verse theory. We know that a 4th dimension means multiple tracks of our reality is possible. Our observation of our present moment is what makes that moment reality - see the photon slit duality experiments to understand that. (Photons exist everywhere along their path simultaneously and it is where we observe them that dictates the moment)

With these things under consideration - it is easy to understand why people think 'simulation' however that is, in my mind, only the result of a language based limitation.

Our language, spoken, mathematical and scientific cannot fundamentally describe manifest phenomena but can only summarize and estimate it. Our maths are at best approximations or more accurately 'simulations' of models seeking to describe the emergent universe.

Because this language is stunted vs. The whole of reality, it is easy to become distracted to see the universe itself as a simulation. However it is our own limits of perception and subsequent limits on description which are the only simulation.

An easy way to comprehend my base point - think of an 8-bit video game using 2 dimensional drawings to represent a 3 dimensional object. Imagine that there are 16 sprites for a single character to make it appear 3-dimensional. This is a simulation of a 3-dimensional object using a 2 dimensional 'language'. It doesn't mean the 3d dimension doesn't exist, it only means the 8-bit video game engine can only describe an approximation or simulation of that concept.