I have been testing the latest version of qutebrowser repository and it works great with youtube, one of the features it has is the adaptability to make your Greasemonkey scripts, the h264ify do NOT work with Falkon which also uses Greasemoney
In this case you have 3 scripts (not mine) but that i use with qutebrowser.
Save this files to /boot/home/config/settings/qutebrowser/data/greasemonkey
To use only x/h264 codec instead of VP9/AV1, that way we reduce the cpu/energy, more than 50%-60%, ideal for older systems, you can also block 60fps videos
h264ify https://pastebin.com/raw/8sTCR69y save as h264ify.js
Since the anti-consumer aggresive adblock blocking, I’ve been using piped.video to bypass the YouTube frontend altogether. It’s adfree, supports sponsorblock and does not require any browser plugins. It’s not always successful with playing the video, but it works most of the time. If it fails, I use yt-dlp to download the video for offline viewing.