I should further clarify, this is a materialist stance. But it's the only practical stance to take anyway. And I will offer the explanation for why this is in first person language because it only makes sense that way. Take it and apply it to yourself:

The materialist stance is taken not because I believe in a strict metaphysical sense that something like solipsism/simulation theory is not true (def true: as real as one's own consciousness), but because even if those were true, the materialist stance and its accompanying theories of modern physics would have the same predictive power regarding what I will observe in the future (well, sort of, at least until I wake up from a simulation, or something like that). I could be a solo mind, but this mind is dreaming of a material world that works according to physical laws, so even if I am a solo mind, I am having the same experience as a brain that exists in true material reality, so it doesn't make much of a difference (except when evaluated for the purpose of philosophical rigor and honesty to oneself).

So "information processing is entirely physical" is strictly speaking an assumption, but it is a good assumption, despite it not having the same realness level as one's own consciousness.