Brightness control not working on Dell Latitude 5420
I have installed KDE Neon User Edition 20.04 with Plasma 5.25 on a Dell Latitude 5420 machine, and the brightness control both through the keyboard hotkeys and through the "Battery and Brightness" widget is not working properly. The brightness level is jumping erratically, and the percentage shown does not correspond to the actual brightness. Many times, indeed, when I push the button to increase the brightness, it actually decreases.
I've attached a short video in which you can see this behavior. In the video, I push every time the key to increase the brightness.
However, if I write a value between 0 and 96000 in /sys/class/backlight/intel_backlight/brightness
, the behavior is correct.vid