I have an ASUS TUF Gaming A15 FA507NV laptop running CachyOS with KDE Plasma. Manual screen brightness change works perfectly fine - however, “On AC Power”/“On Battery” settings for it, as configured in KDE’s power management settings, do not apply when corresponding power events happen.
Other settings, such as power profile or a custom command, do work properly, it’s apparently just screen brightness that does not get applied. I’ve had this issue ever since I’ve installed CachyOS in December - FWIW, it did not happen on my previous EndeavorOS install.
You’re right, I can reproduce this too. It doesn’t seem to be the KDE packages tho, because I just switched to Arch’s (although beta) and it doesn’t work with these either. I’ve tried with linux-cachyos-lts and it didn’t work there too. Can you try linux and linux-lts?
When was this BTW, if you still have some disk space to spare it would be nice if this problem isn’t a CachyOS issue, but I’ll try bisect this somehow if it is.
Just made a fresh (online) EOS install on a second currently unused SSD and screen brightness automatically changes there just fine… Also, the brightness menu has a slider for keyboard brightness control. diffed package lists, but nothing interesting came up other than lack of kgamma on Cachy - however, installing it changed nothing.
P.S.: will have to nuke EOS, sadly, as it’s messing with the boot order. Might put it on an SD card if more testing will be needed…