After I installed ‘brightnessctl’ I added
repeatable_binding_light_up = KEY_BRIGHTNESSUP
command_light_up = brightnessctl s +1
repeatable_binding_light_down = KEY_BRIGHTNESSDOWN
command_light_down = brightnessctl s 1-
to the [command] section of “/.config/wayfire.ini” and now the brightness keys work.