I still have not received the new Fire TV app experience. I have a 4K Max and a Fire TV cube. Does Plex or Amazon make the decision of when a person gets the update? It seems to be taking forever.
consider yourself lucky 
it’s a significant decrease in performance and usability
My 4K Max Gen 2 had a notification in the Firestick settings that an update was available.
You could try uninstall/re-install.
Be aware of a bug with the app on the 4K Max Gen 2. Passthrough for DTS works, but passthrough for DTS-HD does not - there is no audio.
This does not affect all Fire devices, so unknown what will happen with the Cube.
Plex is aware of the problem.
Trust me. You don’t want it. It’s a hot mess. I deleted it and sideloaded the old player.
