Okay then, you should try turning CEC (HDMI Control) off on the Denon. Then, repeat the same sequence of switching on, but only after unplugging the power cord from both the TV and the AVR first. I remember having to do that in the past, before the last several FW update.
With the latest updates, I no longer need to do the unplug trick, but occasionally still have to turn off the AVR and turning it back on. That's still miles ahead than before so I would say ARC is in fact getting better, easier now than a couple years ago.
Here's a screen shot of my Denon's setting. No point to show the TV one as mine is Sony, not Samsung.
View attachment 47312