Please read what I wrote underneath the picture in this post: Library Visibility: Restrict where content from this library should appear - #17 by OttoKerner
Do also know that nothing and nobody at Plex does collect data about which particular file on your server (or servers shared with you) you are playing.
This is laid out here https://www.plex.tv/about/privacy-legal/
(but you need to read it carefully and not jump to conclusions when the text talks about the free ad-supported media, which are available from the Online media sources)
