@mniederkinkhaus It might be installed from a purchase to your iPhone or iPad? If so, I pretended to purchase it from the German App Store in Jamf and the App Catalog shows a bundle ID of: de.prosiebensat1digital.seventv
The Apple TV 4 is a DEP device, so I there cannot be a licence for joyn. In germany the "Joyn" app seems to be installed as a native app of the apple tvs since tvOS 13. But thanks for the bundle ID, it finally works!