Last week, Plex confirmed that its app on iOS, iPadOS and tvOS now integrates with the Apple TV app which means currently watches shows are kept track of using the up next feature within the app. However the integration only applies to the video on demand service from Plex and doesn’t work with any personal content uploaded to Plex.
Like any app that works with the Apple TV app, Siri can be used to find new shows and content and the app will keep track of watched shows.
