after you run an appimage like ./devdocs.appimage does the appimage write any files to your disk or /home folder ?
appimages usually don’t copy files for the system, but, is mounted like a cd, its work because the appimage is a ISO and for this can be executed without write files in your disk or /home.
Everything that in a normal installation would go to /usr is contained inside the AppImage. Everything that in a normal installation would go to $HOME still goes to $HOME.