More info on this - I ran a few tests on my mac and linux systems with chrome/firefox. I highly suspect this is due to gpu acceleration being disabled. https://image.non.io/e7165331-432b-45c3-986e-c2973f12d377.we...
As soon as gpu acceleration is disabled, the webpage goes from 60fps across the three systems I tried to ~7-20fps when software rendering is forced.
I suspect if you go to chrome://gpu you'll find something different from what I have here: https://image.non.io/a47a1b03-1b87-4fd5-92a2-b39e62b1cfd9.we...
Nice research, you are right! Seems that low power mode was on. I have been using the web, Netflix, Apple TV app, and anything else just fine without ever noticing a thing though.
So that all being said, a normal website should work totally fine on low power mode, and this should definitely be a negative on the Opus implementation.