Apparently, importing ~/.config/kglobalshortcutsrc is enough for the shortcut to show up in the System Settings, but not enough to load the shortcut. Disabling, applying and re-enabling and applying again also doesn’t help, and neither does re-assigning to the same shortcut, which resulted in this lovely error dialog.
I thought “meta” referred to the Alt key and “super” referred to the key that usually has the Winblows logo on it. Was I wrong or is the terminology just inconsistent?
The Alt key is Alt. Why would it need another label?
In emacs that is what those keys are called