Like others have stated, this would only hold true if the supposed outer universe to ours has the same properties as ours. So while it may be true that we will never simulate a universe that is equal to ours (with classical computers and algorithms), it doesn’t negate that a computer/device in a universe could simulate an inferior version of the universe.

Take Minecraft as an example. You can make the logic leap and say it’s a simulated universe, and people have in Minecraft created am inferior version of Minecraft with Redstone logic.

So of you can create an inferior version of Minecraft within Minecraft, it’s not much of a jump to think that we could be an inferior version of some outer universe.