Installed the plugin Nextcloud (ownCloud gave the same result). In the dashboard I see the following entry:
"This server has no Internet connection. This means that some functions, such as external storage, notifications about updates and install third party apps will not work. Access files remotely and send notifications by mail may not work. It is recommended to allow this server access to the Internet if you want all features to work."
With the rest of the plugins all the rules. And torrents downloads and Plex is running.