Saw some similar threads previously but no clear answer. How can I get iPlayer on my 360 box to display UHD content? I can view 4K & HDR on the V6’s Prime Video and Netflix apps, no problem, but iPlayer reports (in iPlayer Help > System Information menu) the screen resolution as 1080p only and does not show the UHD symbol for programmes available in that quality. Playback is then not in UHD etc. Same in normal and Beta versions of iPlayer.
360 box is set to output 4k (not Auto)
360 box is connected to a Denon AVRX2300 receiver
Denon connects to a Philips 7334 TV
Able to watch the TV’s built-in iPlayer in UHD as a workaround
Have a read through this lengthy thread to see if anything helps :
iPlayer UHD not working - Virgin Media Community - 4545191
Also - have a look in the iPlayer settings :
iPlayer app settings > Settings & Help > Video Quality > and select Best Quality
Husband, Dad, Gamer, Gadget Lover......