If you’re using an iMacPro SMBIOS, you need to make sure your iGPU is disabled in your bios, and you have no “headless” device ID in your config.
If you’re using an iMac SMBIOS, you would need your iGPU enabled in your bios, and the correct “headless” ID in your config.
That’s it.
There is no specific device ID that I know of between cards (save for some alterations to your config settings on 5700xts and above), but those device ID entries are specific to your cpu if you are using “headless” iGPU. You DO have to remove the boot argument agdpmod=pikera for a RVII.
All details for all of this are in the setup guides of this thread, as well as the dortiana step-by-step guide.
Certainly the simplest is to use the iMacPro SMBIOS method, and I do believe there are performance benefits in editing programs by doing so.