gvfs how to disable a certain backend?
The different backends of gvfs are installed as user services. Therefore you can manage them using systemctl --user.
Therefore you can stop the afc backend using this command (Ubuntu 20.04):
systemctl --user stop gvfs-afc-volume-monitor.service
or disable it permanently
systemctl --user disable gvfs-afc-volume-monitor.service
Note that this only disables the service for the current user. If multiple users are logged in (e.g. via ssh) for the second user the service will still start.