Hello,
I want to replace "System Activity" (which comes with Krunner and is buggy) with "System Monitor" (ksysguard).
In "Global Keyboard Shortcuts" in can remove the shortcut (Ctrl + Esc) for System Activity, no problem. But how do I add an shortcut for "System Monitor"? I couldn't find in the "Global Keyboard Shortcuts" and not in keyboard shortcuts of System Monitor either...

I would recommend setting up a "Custom Keyboard Shortcut" to launch KSysguard here (in System Settings), or alternately set a shortcut on it's menu entry - which can be done via the menu editor (accessible via right clicking on the Kickoff icon, or by running "kmenuedit").

As for me in Plama Shell 5.12.4 in Kubuntu 18.04, I need to reboot the system to apply any new shortcut configuration