I have GIMP installed from Linux Mint repositories.
I cannot find a way of opening the image in GIMP. The Open With command has zero applications show up in the dialog. The only apps I can load the image into are those that are installed via appimage because I can find and navigate to that folder. However since GIMP is repository based I just can’t figure out how to open it from digikam. Open in Folder also doesn’t work as a workaround because the file itself doesn’t get highlighted only the folder gets opened).
If you you just need to find gimp on your system in order to tell the appimage where it is located, then you can user the
whereis gimp
command in your terminal, It will show you most likely /usr/bin/gimp as path.
I think your primary issue is that the appimage is not integrated into you system and thus doesn’t read the installed applications from the .desktop files. Best is to install digikam via the package repositories… Big warning, I’m neither a Mint nor an appimage user.