Backlight doesn't work

Are the settings correct? On the App, Choose Device  then . Setting > Backlight>General  Check the settings are correct. Never had a backlight issue in the 7 months with the device.

Also have you done a restart of the watch doing a FULL powerdown.

Hold in the light button until the watch powers off. Then wait 20s and restart it

That looks correct. Maybe change some settings , such as the brightness to a different level and see if anything triggers some change that may make it work. You should be fine with brightness at 50.

I would also try choosing off , then restarting the watch then changing to on

Not sure if any of this may help..but may be worth a try

50 % would burn my eyes... have been using 20 % for the standard use and for activities, 10 % during night

Great!