One of the most annoying things YT does to me is recommend videos I've already watched. Like I get it, they are perfect for me, exactly the type of video I watch. That's why I've already seen them. And because I don't have the memory of a housefly, I actually remember what the video was about. If I wanted to watch it again, I would navigate to my history or the channel it's from and rewatch it there.
It makes absolutely no sense to me, why recommend videos I've already seen?
I use a browser plugin to hide those videos, but it doesn't fully work.