(I was away a few day's).
Expanding via HDMI on my Tv works better than monitor
, F5 is OK now, however F6 still doesn't work.
Givven your experiment
it seems no ocpn problem.
Do you know how F6 works? I don't think it affects the backlight.
On the laptop I can dim with a Fn combination and I think this does change the backlight. In fact F6 and Fn are supplementarry, you can dim to a black screen.
On board reducing backlight also reduces powerconsumption so that is preferrable.
The Fn on the laptop affects only the laptop, not the expanded monitor
. I will see if I can change the backlight of the monitor otherwise.