I just installed Arch Linux with KDE Plasma on an old laptop. The backlight on the LCD screen works perfectly fine anywhere else, but when loading into the KDE environment, it completely disables. If you have any idea what the problem is, help would be greatly appreciated.
Edit: I directly edited the /sys/class/backlight/<backlight_name>/brightness file and it worked, the backlight is bright and working just fine. To do this though, I had to shine my phone flashlight against the screen to be able to see it, so that I could even edit the file in the first place. Pretty wild bit of troubleshooting, lol.
Edit 2: Discovered the cause of the problem, apparently the brightness controls are inverted with the display on this laptop. 1 is listed as the minimum brightness level, with 7,812 as the highest. The way it actually displays though, is the opposite. 7,812 completely turns off the display, and 1 is the brightest it goes.