I installed endeavouros i3 in my laptop but unfortunately the function keys which control brightness is not working (f2 : decrease brightness and f3 : increase brightness). The function keys worked properly in endeavouros KDE.
In window managers like i3, those keys are bound to scripts or programs that actually perform the work of changing your brightness.
To know what is wrong, you have to look at your i3 config file
~/.config/i3/config to look at which programs are used.