I remember something now. When I first boot with the Radeon VII on my cMP, I released that has a little different behaviour than the RX580.
With non flashed RX580, my monitor has no sign to wake up until OS GPU driver is loaded.
With Radeon VII, my monitor will try to wake up as soon as I power up my cMP. But then get no signal and sleep again until OS GPU driver is loaded.
I think this is a clear sign that the Radeon VII's GOP is somehow different than the RX580. Even it seems "more compatible to cMP" (because able to wake up the screen once power on), but this actually make it can't display the OC boot picker.
Same thing is happening to me. Seems to be something with the Radeon VII...
I thought it might be my boot loader, so I went through the hustle of going from 140.0.0.0.0 to 144.0.0.0.0 but no change.
Sadly my bootcamp drive is still stuck in legacy and I can't boot into recovery to transform. Its not a very pressing matter. I guess I can just reinstall Windows sometime. Or has anyone got a different Idea?
Anyhow, boot picker would be nice...
Very thankful for the guide! Hardware acceleration is a charm!