Worth noting: A Pi 1 will decode 1080p h264 video flawlessly. I used one as a media center for a long time, running OpenELEC (now LibreELEC). Moving around the UI was a bit sluggish, but video playback was smooth.

YouTube is an absolute clown show. It's so bad that I'm certain Google devs are actively making it terrible on purpose. I use Newpipe on an older (but not that old) tablet. Whenever Google breaks Newpipe and I have to use a browser, it takes like 30 seconds just to load the page.

Decoding video is trivial when you have hardware decoders.

Are they even pushing H264 to the pi? Or is this more of their “you’ll take WebP and like it” stuff.

I had this on my old laptop too, it would really struggle with HD YouTube, but if I copy pasted the url into VLC or MPV it would play just fine.