Interesting! Do you have webgl disabled for incognito or for chrome in general? I wonder if it's trying to do software rendering.
FWIW, I have literally the exact same configuration (M3 air, google chrome). Here's a recording on mine where I'm seeing 60fps: https://non.io/video/video-3587018401.mp4
Unless it is something with the playback on my end, your animations and scrolling are a bit jerky too.
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Mine doesn't stutter on on Firefox on M1 Max, but it pins 7 cores the entire time the page is open, not just while loading. It also uses 50% of GPU in addition to that.
Edit: The argon built site pins 1.3 cpu cores. The Sol 6.1 site uses 0.18 cores.