Over the last several months, YouTube has been phasing in a new player design, and the version of it that gets embedded in other websites is abysmally bad. The biggest problem is that the player controls appear if you hover over the video for even a moment, and then they stay onscreen for four whole seconds no matter what you do — obstructing your view of the video you're trying to watch.
Particularly annoying is the big pause button that appears in the very middle of the video, reminding you (as if you didn't know) that you can click the video to pause it.
You had one job, YouTube! Let me watch a goddamn video! And you failed!
Anyway, I fixed it. You can hide the pause button by adding this line to your uBlock Origin config:
youtube.com/embed##.player-control-play-pause-icon
Similarly, you can add this line to hide the "more videos" blob (not sure what to call this UI element tbh):
youtube.com/embed##.ytmFullscreenRelatedVideosEntryPointViewModelButton
And if you just want to burn it all down, there's the nuclear option which hides absolutely everything except the video itself:
youtube.com/embed##:not(:is(video, :has(video), cued-overlay, :has(cued-overlay), cued-overlay *, .ytmVideoCoverThumbnail, :has(.ytmVideoCoverThumbnail)))
Wait, what's that you say? You don't have uBlock Origin installed? Well, the same block rules will probably work in other ad blockers. Otherwise, you can get uBlock Origin here.