I wasn’t sure whether this issue is related to Plasma or a specific version of it used by Tumbleweed, so I wasn’t quite sure what the right forum would be. Decided for this one then.
I have both Ctrl+Alt+T and Meta+Enter set as a shortcut for my standard terminal emulator. This worked until I switched to Cool Retro Term as standard terminal emulator. I thought it might be because of this, so I switched back to Konsole, after which it still wasn’t working. I rebooted, it still wasn’t working. I can call both of them manually though.
My system had all available updates applied all the time.
EDIT: I just tried setting another option (Search) in the “System Settings” tab of “Global Shortcuts”. This one didn’t work either. All other shortcuts work though.
I did that, with the result it still wasn’t working, and the shortcut of pressing Meta for the Kicker (the application launcher) breaking (and of course me having to redefine all my shortcuts). Somehow the “System Settings” tab also vanished from the Global Shortcuts. I then realized I had to activate “Launch Konsole” in “KmenuEdit” of the Custom Shortcuts, and set that value to Meta+Enter (which I prefer over the default Ctrl+Alt+T). After setting the shortcut for activating the Aplication Launcher to a more or less random value (Meta+M), the default Meta shortcut also started working again for some reason, while removing it would break it.