Systemindstillinger/Tastatur
Appearance
In this section you can manage the settings for your keyboard.

Aktivér at Ctrl + Alt + Backspace standser X-Serveren
Under
tab, make sure is enabled. Then look in the list below for "Key sequence to kill the X server". Under it, you should be able to check . Once done, click on .
More Information
- KDE official documentation
- Keyboard configuration (Arch Linux wiki)