Not sure if you found a solution to this however i've spent 2 years almost trying to work through issues with this Denon to Samusung nonsense and limiting HDR pass through or Xbox or PS4 pro optimum video pass through.
After numerous calls, emails, live chats with both Samsung and Denon, i have found a work around that for most part will give you exactly what you want or at least free up some HDMI ports on your TV.
Depending on your Denon model (mine is the AVR x3600h) and i have the Samsung 75"Q9FN i have had nothing but issues in loss of signal or intermitent faults/no option for HDR suggesting its not supporting the formts when it does.
Anyway on the output from Denon AVR rather than using ARC, use monitor 2 output and or zone 2 if you have one. Connect this into anyother input on the TV except ARC (usually HDMI4). Bang no issues with sound from your devices or reduced picture quality/limitations. The down side is ARC isnt available, however that would only be an issue should you be watching apps via the Smart TV itself. For me that wasnt an issue because anything i want to watch via sound i would prefer to have connected straight to the source (AVR) then to pass through video to the TV.
Clearly it seems to be a handshake issue on the ARC port that either Samsung or Denon need to take responsibility for. Ideally both fix it however i can confirm if i connect my PS4 Pro now to any port on the denon and then connect the AVR to any port on the Samsung one connect box excluding HDMI 4 than i get enhanced picture quality. (also if your Denon AVR receiver has an option turn video output to enhanced and Same for samsung UHD option turn that on too).
Firestick 4k also has no issues with optimum video and sound too in this set up.
P.s there is an added bonus. The AVR being connected to Samsung on another port also switches TV signl mode to game mode automaticallt too just as if it was connected to the TV directly. It never done this before previously.
This is a much more acceptable work around until both get their finger out and offer a fix or update. You can get ARC via optical and worst case pretty much any App you would view on your smart tv you can get via most common Bluray. DVD PS4 Xbox etc. devices so really not much use for ARC in the meantime.
Let me know if this works, before you invest in more HDMI cables, and bang your head off any more walls. Thats how i feel.
Gerry
