Wouldn't another option be to use the system package [0] or is the version too old? Or use the Flatpak [1] (or NIH-flatpak [2]), which is probably a better fit than AppImage for GUI programs that sit on top of a heavy toolkit.

[0] https://packages.ubuntu.com/search?keywords=digikam

[1] https://flathub.org/apps/details/org.kde.digikam

[2] https://snapcraft.io/digikam