New comment by FollieHiyuki on void-packages repository

https://github.com/void-linux/void-packages/issues/30342#issuecomment-823045457

Comment:
Could you verify these?
1. Is your user in `video` group?
2. `brillo` works for me here. But you need to store the brightness value first (`-O` option) then use `-I` to restore it. There is no need for a service though you can easily run this at boot manually.
3. "dbus does not work in xorg automatically" --> Have you enabled the dbus service? Not really necessary with some xorg WM/DE but you can always use `dbus-launch` or `dbus-run-session` as normal user.
4. "polkit agent won't work" --> Have you installed 1 of the agents from the repo?