I now remember that on a moment of reading and testing how to use the clip region I used the Alt+B combination but not observed a behaviour in that moment.
So it is not a bug, sorry.

I just pressed Alt+B and it dissapeared!

Same here. My keyboard stop responding after using BlenderKit for a moment. Mouse works as expected. And keyboard is working in other apps correctly.

Sorry, 3 faces per side (right and left sides). What I mean is that there must be enought faces but you need some special case to discover it better. The default cylinder is OK with 32 vertex.

I was just thinking about this. There are an option called "volume". And it does some like the "face" option. "Volume" is OK as actually works because it is clear that only the volume is taking in account.
But actually choosing "face" is working like a "surface". Because it is something similar to "volume" but per face (or, surface as the term fits better).