After an update to groupfolder 3.0.0 occ seems to get broken completely by this app version i.e. including the maintenance command. See the 3.0.0 upgrade breaks occ #395 bug report.
You may try this workaround at your own risk and after your own careful consideration as admin:
- disable the app Group Folder in the app view of the GUI as admin
- change to the command line of the NC server and follow the below procedure.
cd ~/my-nextcloud sudo -u www-data php /var/www/nextcloud/occ maintenance:mode --on sudo ls -la /var/www/nextcloud sudo mv /var/www/nextcloud/apps/groupfolders /var/www/nextcloud/apps/groupfolders_3-0-0.backup wget -q https://github.com/nextcloud/groupfolders/releases/download/v2.0.4/groupfolders-2.0.4.tar.gz -P . sudo -u www-data tar -zxf groupfolders-2.0.4.tar.gz -C /var/www/nextcloud/apps sudo -u www-data php /var/www/nextcloud/occ app:enable groupfolders sudo -u www-data php /var/www/nextcloud/occ maintenance:mode --off
This procedure downgrades to groupfolders 2.0.4 and should allow continuity to the NC environment.
One may recall former troubles like Groupfolders 2.0.0 breaks NC 14 and NC 15.