I set activity backlight always on [during activity no timeout, gesture on so it never goes out once lit],
(as it takes for it too much time to light up and mid activity I want fast access to data).
During an evening run I've activated the flashlight [double click on upper-left button, the controls, both for ON and OFF]
After I deactivated the flashlight I noticed the backlight was turning off every time I'm not looking at the watch (this is as resetting timeout) ["not looking" = gesture controlled].
It continued till the end of the run.
On next activity the backlight acted as expected.
I didn't test it on other activities (beside running) but I guess there is a good chance it's everywhere.
(Why would flashlight sabotage backlight?! Did you keep the software from when the backlight WAS the flashlight, and didn't uncouple it well?)
Fenix 7pro, 16.22
