After using KDE Menu Editor for several hours and filing a bunch of bugs, I still can't quite figure out what that checkbox does.
Git commit 8997b0077b67012867f24b92101cd8a802587b26 by Nate Graham. Committed on 26/02/2021 at 16:29. Pushed by ngraham into branch 'master'. Rephrase "Only show in KDE" for accuracy and clarity KDE is no longer the name of a desktop environment; let's rephrase this to use the actual name of the DE and also be a bit clearer about what the setting actually does. FIXED-IN: 5.22 M +2 -2 basictab.cpp https://invent.kde.org/plasma/kmenuedit/commit/8997b0077b67012867f24b92101cd8a802587b26
I saw the change to "Only show when logged into a Plasma session", but how could I see the launcher menu items when I'm not logged into Plasma? Does the launcher appear somewhere else?
Unless you check this checkbox, then yes, these apps can appear in other desktop environments' launcher menus as well. There's a cross-desktop standard governing this, precisely so that any chances to .desktop files that you make in one DE are reflected in other ones.