I've had the problem with sky sports uhd looking dull and flat and found a solution, sorry if this has been said before.
I discovered that the Puck has created another input, see picture.
TV naturally default to Hdmi 1 and picture is rubbish, but it I manually select Sky Hdmi 1 picture is perfect.
Hopefully will help someone
My setup is sky puck to soundbar which allows 4khdr passthrough to tv