Many performance problems on YouTube are because they now force everyone to use the latest heavy codecs, even when your hardware does not have acceleration for it. I have a laptop that is plenty powerful for everything else and plays 4K h264 no problem. 720p on YouTube on the other hand turns it into a hot slate after a minute and grinds everything to a halt.

There are browser extensions like h264ify that block newer codecs but WHY??? Is nobody at YouTube caring about the user experience? It’s easier and more reliable to just download the videos.

Nah, their page and player are ridiculously heavy and slow regardless of the video codec.