I fix it last night. Check updates, and maybe install light
and change ~/.config/i3/config
# Screen brightness controls
bindsym XF86MonBrightnessUp exec --no-startup-id light -A 5%; exec notify-send 'brightness up 5%'
bindsym XF86MonBrightnessDown exec --no-startup-id light -U 5%; exec notify-send 'brightness down 5%'
Maybe reboot