The desktop integration icons for The Linux AppImage are missing.
I believe the fix is as simple as adding the icon alternatives for the missing folders below while building the *.AppImage:
AppImageLauncher changes the file’s name and moves it to an installation folder with a different name. I did a quick test by adapting that script with the new Appimage filename, but it did not work even if the script was successful. The cause is probably related to the id added by AppImageLauncher for the icon, but it must be investigated.
Adding the icons above to the build would help create an AppImage that works for both cases. It will work for those who want to use AppImageLauncher (which has advantages, such as centralizing all AppImage in one place and easy uninstall, for example). And those who do not use AppImage can use that script.