This userscript will force all videos to use the h.264 codec rather than VP9/AV1.
This is a simple script to block AV1 and VP9 codec in youtube to reduce the cpu and resource usage.
NB : It has a drawback and that is the highest video quality is limited to 1080p
It works with every mv2 extension.
This script also works in manifest v3.
But it needs ScriptCat as the userscript manager.
Chrome Web Store - ScriptCat