This will be my last entry into this thread. What is amazing is that almost everyone has been correct almost all the time. I mean this as high praise for all the effort and work on this "puzzle" that is missing so many pieces.
I saw where "Priitv8" posted his /her / them's CPU specs on what has to be a 2019 27" iMac and totally blew up my theory that ALL 2019 iMac 27" i9's had zero onboard graphics. I am guessing again if they run out of the "KF" processor with no graphics they switch to the "K" with graphics. That though is one BIG crap shoot. The one I just returned was a "KF", "KF" is listed as the Apple processor used on this machine and also I saw where HP, Dell and others are using the "KF" processors also.
Now the part that is for me "out of my depth". Even if you have the "K" series the Apple we use still do not have HDR Displays. Sure they are 5k, 4k Retina eye watering displays they still have no HDR. That is
High Dynamic Range of colors. Also and I could be very wrong but unless you can "trick" your 2019 i9 iMac to think that it is running on battery the computer will default to the Vega 48. The MacBook Pro goes to the intel GPU on battery for obvious reasons and I am not sure if it can be override. Last is the FACT that 4K UHD DRM

igital Rights Management" only works as a whole if
every component is 4K UHD DRM certified. That means the cables also. So first thing is to get an external monitor that fits all the specs. And so on....
Back to Apple. I am sure of one thing and that is they are not trying to mess up our wanting to play 4K UHD DRM media. The studios that made this crappy mess already. Microsoft OS computers all have the same compatability problems. The thing that they use is intel SGX tech and Apple will not go near it. It is Intels version of the "T2" chip. It handles security and handshake functions that help unlock the DRM side of the problem. It has been riddled with flaws and that might be a reason that Apple decided to not risk security over playing a 4K movie. I myself rather have the "T2" chip. I am sure they are working on it. It can be fixed through the GPU and as I said an external Monitor.
I do not care what anybody claims about what Windows 10 can do. IF any component connected to their Windows 10 computer system is not 4K HDR DRM compliant it will not work. When we run Bootcamp / Parallels / Windows 10 we may be seeing a movie, Tv show, we just are not seeing it properly.
Now I am going to just have fun doing all the things it can do. Wait a few months and see how Catalina effects these obstacles.
The one thing I can say about Apple is that I no longer have an extra bedroom full with all the crap that was "Windows compatible" that I could never get working!
Cheers!