I would recommend you give iMacPro1,1 SMBIOS a try. On a real Mac, this profile only has a discreet GPU so it should work with your RX 480. I am using it with a Vega 64 and haven't had any issues.
Don't inject that device property since you have the iGPU disabled in BIOS.
In BIOS, try looking for in Settings/Advanced/Integrated Graphics Configuration. In there IGD Multi-Monitor should be disabled. That is your onboard graphics.
Initiate Graphic Adapter should be set to PEG in that same section.
Try out the attached EFI folder. On your OS drive, make sure the path to EFI is set correctly. When you mount the EFI partition, the folder structure should be EFI (Partition)/EFI. As long as you paste the attached EFI folder in the EFI partition, you should be able to boot from the hard drive...
Based on your About Mac screenshot, you are not using iMacPro1,1 profile. If you were, it would show as iMac Pro (2017). Compress (zip) your EFI folder and when you're typing your reply here, you'll see the Attach files option. Use that to include the compressed EFI folder in your reply.
I have a LG TV connected to my desktop with an HDMI cable. Whenever I turn the TV off at night, the next day, when I turn it back on, I get a "No Signal" message. I then have to unplug/re-plug HDMI cable to get it work. This had never been an issue before. It just started happening the last...
Is it possible to use a 1080p display on a laptop without having CSM enabled? On my laptop, if I disable CSM, the OS boots to a garbled screen. Is there any workaround to this?
It appears that the issue only occurs when resolution is set to 1920x1080. If I set a lower resolution in...