Blank page after nextcloud upgrade web interface V25

I hit to update the server from the web interface and for a moment I exited the tab and when I came back the page was blank. I don’t know exactly what I should look for or do, I don’t have any backup done unfortunately.
Nextcloud is installed in a proxmox container, it also has webmin.

Can it be solved? Do I lose the data?

No. There is a datadirectory with all files. You find the path in config/config.php. Maybe now is the time to back up this directory. Also you can backup your database e.g. MariaDB.

To solve the problem maybe you can execute the upgrade-command form command line. Maybe someone here can post a command for proxmox container.

What is the command, as I keep looking for it and can’t find it? (and it is put in the console of the proxmox)