We are obviously in a simulation, at least two layers. The fact that we are built up from a set of consistent rules and atoms, basically pixels, rather than an open and free canvas, is direct proof of one of these layers. The second is that every single experience a human has is inside the brain rather than "out there", as it's a model synthesized from raw sensory data. You can't directly experience "out there".

The question is not whether we are in a simulation, but rather is there an experiential reality outside of this simulation, or did the simulation pop into existence from nothing.