@ r u willin to help or am i botherin u ???
you are not bothering me, absolutly not, but i try to make understand you that i cannot help you if you don't help me. i have a day job too, i cannot pass my time to try to understand what happens on your machine. When you have a trouble you need to describle the trouble as precise as possible with the maximum of information that you can recolted; i don't know your skill too.
Anyway, about brightness
have you the package upower-nosystemd installed? i think so. look for the package powerdevil too if it installed on your system.
honestly i never used this features on kde, and i don't have the hardware to test it.
after a few research, the control of the brightness on kde seem to be possible by the battery icon on the task manager when you click on it. If you don't have, you can try to make a rules for polkit like this in /etc/polkit-1/rules.d/10-backlight.rules and put on it these following lines :
polkit.addRule(function(action, subject) {
if (action.id.indexOf("org.kde.powerdevil.backlighthelper.") == 0 &&
subject.isInGroup("users")) {
return polkit.Result.YES;
}
});
after adding this rule i have the possibility to control the brightness when i clik on batterie icon(you need to reboot to make this rules available). Changing the value do nothing on my hardware, but this is particular about my hardware
hope this help
i saw many many people rule the brightness by creating shortcut : system configuration ->shortcut
i can help more about this, you need to make your own research about it because i don't have the correct hardware to make test.