I was able to boot with 6800xt installed, I had to enable CSM for that, without it computer wasn't booting.
I wonder if there is a way to display GPU temperature\frequency in macOS, I remember I've used fakeSMC for my Vega56, do you know any other way?
Also, I remember that with Clover I had to change from 18.3 to 18.1 when I've removed my dGPU, do I need to do the same with OpenCore? macOS identified it as iMac (21.5-inch, 2017) now, I wonder if I need to change that? The reason why I ask is that with 18,1 macOS identifies my CPU correctly as 6-core i7, but with 18,3 it appears as 6-core i5. Do I need to be concerned about that? In Catalina it was i7 in both SMBIOS versions.
And the last question, it takes forever too boot macOS, a minute or so, during this wait time I see that the hard drive is used a lot, so I am guessing that it is actually doing something, however my Clover Catalina was booting within 15 seconds or so. (Disregard this, I found the reason, and that there is no solution)
As usual, a huge thanks for your help. This hack brings me a lot of joy, and that is all possible because of your help Chef!