What? Plex is not one of those open source, self-hosted, privacy-centric services. Plex can do whatever the hell Plex wants with your watch history, because you agreed to their broad terms of service that said exactly that when you signed up. You chose to run your traffic and authentication through Plex servers because it’s convenient, not for privacy reasons.

If you don’t like it, use Jellyfin. I’m personally looking into moving, as Plex seems to be getting slowly shittier.