This only applies to classical computers not quantum, some combination of both, or by some means of computation we haven't discovered yet.

Doesn't this simply suggest that the reality that is simulating our universe would have to be fundamentally different than our own?

No: https://www.scottaaronson.com/blog/?p=3482.

I remember reading something a decade or so ago which said that to simulate the entire known universe, even using selective windowing, would require more energy than the entire universe has. Wish I could remember the source.