I used my notebook without charging until it went under 5% battery (that makes the brightness very low) and then it crashed into the kernel, then I forced a shutdown but the screen is still at low brightness even fully charged. Is the battery settings designed to revert all battery changes upon charging beyond the percentage that caused it?
Noticed that this is a setting disabled by default, so even though I disagree, it's intentional.
It seems there is a bug after all. The bug seems to be that the brightness only changes when the charger gets connected. Which means that if your home's electricity is low due to storms, then the notebook goes to low battery, the brightness doesn't go back to normal because the charger was always connected. I've unplugged and plugged the charger again and the brightness returned.
The change to "With energy adapter" setting should happen when the battery is receiving sufficient electricity.
Seems like the computer has to shutdown due to low battery while the charger is connected but giving insufficient energy for this issue to happen after properly charging.
Created attachment 176326 [details] I had to disconnect and reconnect the charging cable to make the system increase brightness.
Created attachment 178886 [details] Issue on Plasma 6.3.1
It's very easy to reproduce this issue by having 10% or less battery, suspending the system, plugging the charger, then logging back in. The brightness should be low even when charging the battery.