what does this mean

was just messing around in one of the games I played when I noticed this

I don't know what this is, the first encounter I have with this, and I don't know what it does/mean

The arrow in the top image means only legal move.

The red banner in the bottom image is one of those site glitches that pops up from time to time.

There have been other posts with the classification error and it seems it always happens at the end of a variation.

the red pop-up means the move was a checkmate or stalemate.