Great question and the answer will change, as the boxes can be updated, some smart apps will be removed and some upgraded or replaced as time moves on, but as of May 2024 you can currently use these apps.
Netflix
NOW TV
Channel 4
BBC iPlayer
ITVx
My5
UKTV Play
Disccovery+
APPLE TV+
Prime Video
Great player / Pop Player
WATCH FREE TV
And a few Sound Radio Apps.