Mobs of any sort aren't spawning in mountains beyond a certain elevation. I was living in a mountain yesterday in a test world and nothing whether hostile, passive, you name it, was spawning after a certain height. I'm guessing it has something to do with elevations not registering as places where mobs should be spawning as a result of the world height increase.
Yeah on PS5 this issue is still a thing so it's definitely still relevant and in need of fixing. It hurts my eyes to try and see the tiny interfacing, otherwise I'd just deal with it.
As of the release of Caves and Cliffs Part II, this bug remains unresolved.