I installed thunderbird via zypper. It is behaving correctly, unlike the one I installed from flatpak (a long story, but I decided to uninstall that instance). sudo zypper in thunderbird installed but gnome refuses to launch it from the start menu. It runs if I launch from a shell but if I type it in it fails to find the app.
Can anyone help me to “register” this app so I can pin it to Task Manager etc. Sorry if I don’t have the terminology correct, I have been using only KDE Plasma with Slowroll for a long while now, and vocabulary is sometimes different from one DE to another.
First, try logging out and in again on Gnome, which will force it to refresh the menu (although it usually does so as needed). If that doesn’t work, my guess is you have some files still lying about.
A little background: application menus are built using a *.desktop file for each application, that is in the share/applications subdirectory of, in order of preference, your $HOME/.local directory (or $XDG_DATA_DIR instead if set), then any of the directories listed in $XDG_DATA_DIRS, in order. When Gnome populates the menu, it seems to test each of these files, and will not show it in the menu if it looks like it will not work. In contrast, KDE Plasma does not seem to test, it will just show the application anyway, but then clicking on it may produce an error. That’s probably why it seems invisible on Gnome.
I suspect you have a broken *.desktop file in one of these directories. It could be there from an incomplete Flatpak uninstall, or by using “Edit Applications…” in KDE, or from a third party app for editing menus.
Try running this command, or something like it, to find relevant *.desktop files for Thunderbird: