In the default applications settings, is it possible to set the default email client to an AppImage? I'm using a Tutanota Desktop client for Linux that's an AppImage file but I don't see a way to use it as my default email client & when I search online for solutions I just see articles & forum posts explaining how to integrate AppImages into the DE but I already know how to do that so I was wondering if any one knows of any solutions.

EDIT: I was told to "as root, open this with your text editor: IE: sudo nano /usr/share/applications/defaults.list change it: x-scheme-handler/mailto=thunderbird.desktop x-scheme-handler/mailto=/path/to/myCoolEmail.appimage" and "protocol says if it is not installed at /usr/local/bin or /opt move it there." but when I did as instructed it still didn't make it where I could choose the AppImage file from the default applications settings. Is it not possible to do this? Would this suggested solution be a good workaround despite not making a difference in the settings GUI?