On Mac, I wrote a config [1] which uses `ddcctl` [2] cli tool to sync both brightness and volume using keyboard buttons. It worked quite well, although I haven’t used it for a while. I guess similar idea could be extended for linux too.

[1] https://github.com/prashnts/dotfiles/blob/master/etc/hammers...

[2] https://github.com/kfix/ddcctl/blob/master/README.md

Edit: Just noticed further down in the comments that an app exists for it now!