Try connecting it to the TV directly to rule out the avr.
It's probably the Denon.I see lots of talk on this but I can’t for the life of me get 4k and HDR to display on my 65inch LG C9 Oled. I have turned on the UHD deep color on the TV as well. I’m using hdmi 2 input on my tv. PS5 original hdmi cable is going into my Denon x1600H and Denon HDMI out to HDMI 2 input on the TV. Could it be the Denon? Just updated the LG firmware as well. Can it not do both?