Holy crap this feels massively better.
That's exactly it, when I block AV1, it shows up only 4K HDR in Chrome, when I unblock / refresh, 8K HDR appears. I have to find that video someone posted asking if it crashed the MBP, that one definitely crashed my mbp when I tried to play it. If you have example videos you'd like me to try just paste them in. However I have no such extension on Safari, it doesn't even give me the choice probably to what you mentioned.
I'll check more videos, Chrome feels better? but I always thought chrome felt snappier on scroll in 12.0.1 than Safari.