I do too use Firefox on Linux, 4K videos seems to work fine for me, but I've never been able to download higher than 1080p with yt-dlp, seems it's just not available without DRM as far as I can tell, so now I'm curious how exactly you've been downloading that?

yt-dlp + 4K works fine for me. The only special thing I remember doing is adding the impersonate feature (which it prompts you to do if it needs it). In other words, instead of `uv tool install yt-dlp`, run `uv tool install yt-dlp[default,curl-cffi]`

The version in the Arch repos does not include the impersonate feature.