Librem 15: Fn keys debian bullseye

I have a Librem 15 running debian bullseye.

The Fn Esc key works to suspend and Fn F10 works to cycle keyboard backlight brightness, but Fn F5 and Fn F6 (display brightness) don’t seem to do anything.

Can anyone point me to how to get the desired Fn F5/6 functionality on the Librem 15 under debian?