After installing a bunch of different versions of GIMP over the months on Linux Mint, I'm somehow stuck with one beta GIMP in my Cinnamon's start menu that I can't get rid of by right clicking on it and clicking uninstall.
As per usual on Linux, when something doesn't work, it just doesn't work silently, with no error dialog shown. I have no idea how such good programmers keep making this same infuriating mistake of quitting silently when things don't work. SHOW ME THE ERROR.
On the software manager, I can't find any GIMP's installed. It's worth noting that there is a separate system and flatpak GIMP, and I think the "Uninstall" button won't appear for the flatpak unless you click on a dropdown to switch to the flatpak version from the system version. But I checked both and I can't uninstall anything via the GUI.
The solution was to run the following command via the terminal [how?]:
flatpak uninstall gimp
This will find that GIMP flatpak that somehow Linux Mint silently failed to install repeatedly and let you finally uninstall it.