What hardware do you run, and do you still need help?
Arch is very different from Debian based Linux, where even the same packages can have different names, so using the Arch Wiki for non Arch based Linux distros is not recommended.
I don’t know which drivers are preinstalled on Ubuntu, and some people also seem to have problems with frame drops (e.g. https://askubuntu.com/questions/1520102/why-do-i-get-so-many-frame-drops-on-wayland-with-youtube-playback), so no idea where to begin to help.
Sad to see you go. Every Linux user is one less person relying on our corporate overlords.
If you would like to give feedback to Brave, you can do so at https://github.com/brave/brave-browser/issues, where you should include your OS, hardware, and installed drivers.
Going with Arch as a first Linux is certainly a choice, and I’d guess a random library is missing. If you are still interested in Linux and it’s also happening in other browsers, I would recommend trying other distros with more “mainstream” appeal (e.g., installed desktop environments and drivers), such as Fedora, Mint, or CachyOS for rolling releases.
I’m also quite new to all this stuff, so if I’m wrong on something, please tell me.
Ergänzend zu den anderen Kommentaren: Eine weitete Ansprechstelle die ich noch im Kopf habe sind die Land Grazien https://land-grazien.de/. Sind (wenn ich mich richtig erinnere) vor allem auf ländliche Regionen in Schleswig-Holstein spezialisiert, machen aber sicher für alle Fälle das was sie tun können.
Wünsche euch mit aller Kraft, das ihr es schafft und durchhaltet.