Isolate and Disable Incompatible Third-Party Applications

If the maintenance mode is triggered by a specific app, you must identify and disable it to allow the core system to boot.

1. Navigate to your Nextcloud data directory and open the nextcloud.log file to identify the specific app causing the fatal error or migration failure.
2. Access your server via SSH or the Docker container terminal.
3. Execute the command sudo -u www-data php /var/www/nextcloud/occ app:disable <app_name>, replacing <app_name> with the identifier found in the logs.
4. Run sudo -u www-data php /var/www/nextcloud/occ status to confirm the system is no longer reporting an app-related upgrade requirement.
5. If the system remains in maintenance mode, proceed to run sudo -u www-data php /var/www/nextcloud/occ maintenance:mode --off to clear the flag.

Sources