Well, I’m an idiot. Seriously considered deleting this post, but in the hopes that it helps someone with the same brain fart as me…
Quite some time ago, I was experiencing green artifacts on video playback on a very specific local video page (UI3) for a network video recorder called Blue Iris. At the time, the workaround was to disable hardware acceleration.
I was certain that everything was back to the default settings since that’s what it reported under brave://flags hardware acceleration. However, going to settings, system, hardware acceleration was still turned off. Once I switched it on, CPU dropped back down, and video is smooth.