I use Apple TV to get iTunes 4K and to get Dolby Atmos from Netflix 4K.
I have the Netflix 4K app on my TV, but I don't get Dolby Atmos over ARC. eARC would solve that problem, but that would require that I buy a new HDMI 2.1 receiver to support eARC, and a new TV as well.
It's pretty much the same for me. I also have ARC disabled on my TV because for some reason that feature is tied to the one that allows powering on/off the TV to power on/off the receiver and switch the input. I like ARC, but can't stand that auto powering feature because there are too many cases where it won't do what I am trying to do and makes it almost impossible to do what I want (ie turn on Apple TV just to stream music...Receiver and TV turn on, but I don't want the TV on so I turn it off, then the receiver and Apple TV turn off too...) I've found that in general I much prefer to just manually control things because far too often the automatic control gets it wrong. But turning off that power control forces me to give up ARC too...