I wanted to try isd so I downloaded the app image and chmod 755. It errors immediately. I realize this might be fixed by giving it sudo but I wanted to try it for managing user-mode systemd services first before running a new app with sudo right away.
$ ./isd.AppImage
./isd.AppImage: cannot write uid_map: Operation not permitted
$ ./isd.AppImage --help
./isd.AppImage: cannot write uid_map: Operation not permitted