Ps4 Minecraft dark border?

I'm currently playing Minecraft and for a while now there has been a dark border on the edge of the screen that is normal, why is that, can you make out that it comes and goes away on its own after a while and then comes back.

It is not the case with me. It could be some kind of screen saver or it could be just the TV. Otherwise I would have two more questions: 1. Is it only for Minecraft? 2. Is it only in a cave or also outside?

It happened for the first time today so I don't know if it will happen in other games as well. I was only in the cave today outside it has never happened before.

The rand has been new since 1.16 … But that it comes and then goes away is new to me?!