Run Database Upgrade and Maintenance Repair

If the instance is stuck because a previous update failed to complete, you must force the database to finalize its migration.

1. Access your server terminal.
2. Run the upgrade command: sudo -u www-data php occ upgrade.
3. If the upgrade reports completion but the site is still stuck, run the repair tool: sudo -u www-data php occ maintenance:repair --include-expensive.
4. Restart your web server service (e.g., sudo systemctl restart apache2 or sudo systemctl restart nginx) to clear any remaining cached states.

Sources