I can confirm this same problem occuring on my Denon x4700h. I have it hooked up to a Samsung UE55KS8000, and a raspberry pi5 with libreelec on it. It seems Denon does not agree with the Pi 5's take on 4k60hz resolutions.
When the pi5 resolution is set to 4k60hz i get no display though the Denon on any of the HDMI inputs. Tried 3 different cables. When i plug the pi directly into the tv, 4k60 works smoothly with HDR, so it is definately an issue with the Denon AVR. When i set it to 4k30 the denon will display the pi5's output, but the image quality seemed off, possibly an issue with HDR. I will need to do some more troubleshooting on this.
My current workaround is that i have hooked up the pi 5 HDMI output directly into the TV, and looped an SP/DIF optical cable back from the TV to the Denon AVR. Having activated HDMI CEC on all three devices i can still have the pi5 wake and shut down both the avr and tv. Only downsides are two cables running across the wall to the TV, and the whole HDMI feature on my AVR being bypassed, making switching to different sources besides the pi a bit more of a hassle.