I’m way late with adding this. But I opened a case with AMD and their response was . . . informative:
"I regret to inform you that after further investigation, it has been confirmed that PCI Passthrough is unfortunately not supported in any configuration for the 7900 XTX. Although some members of the community have managed to find workarounds, it’s important to note that these are not officially supported or tested by AMD.
To answer your inquiry about a flag or registry option to enable video output, I can confirm that this is not available. There are currently no plans in place to support passthrough at this time, and I understand that this may not be the news you were hoping to hear."
Translation: ‘you bought our highest tier consumer card but we don’t want to support pcie passthrough on it. And that problem you are having with vDisplay autoenabling we don’t care about, so tough luck.’ Needless to say I’m not planning on buying another AMD gpu in the forseable future. And this response was AFTER I noted my nvidia card works properly.