I'll bet chrome://gpu either shows "WebGL: disabled" or "WebGL: enabled; WebGL2: disabled". I think `ignore-gpu-blocklist` in chrome://flags should affect WebGL.
FWIW I'm running Chrome on Linux with hardware rendering force/explicitly enabled for both video and rasterization (`enable-gpu-rasterization` in chrome://flags - don't think this affects WebGL), and it all works great (notwithstanding terrible thermal design) on this fairly old HP laptop w/ i5 + HD Graphics 4000. (The GPU process does admittedly occasionally hang and need killing so it restarts, but that's about it.)
Getting video decode requires --enable-features=VaapiVideoDecoder on the commandline as well, or at least it did in the last version of Chrome, I haven't checked if this is no longer required.
If poking `ignore-gpu-blocklist` doesn't work, what does chrome://gpu show in Chrome, what does about:support (and possibly about:gpu? not sure) show in Firefox, and what GPU and OS are you using?