Mine is still HD thought it looks identical to the Paramount + app.
Do you mean the Paramount+ app on your AppleTV 4K?
Mine (a 2021 ATV4K) indicates 4K for those (on their info pages anyway), but no HDR though, so I'm not completely sure they're really streaming in 4K since I don't have X-code or whatever extra enhancements installed/enabled to be able to tell.
_Man_