ok try this one:
Also add radpg=15 (and -radcodec might not be necessary) under nvram section. Do a nvram reset before booting into macOS by pressing the space bar in OpenCore GUI if the nvram reset isn't available by default.
If you look closely you can see that the Dock and the Menu bar are not transparent which means there is no Hardware Acceleration which means the web deriver doesn't work at all, it only detects the GPU model and that's it.
There are no Web Drivers beyond High Sierra
I regenerated the SSDT-GPU-Spoof.aml and I removed the device properties.
My SSDT addresses the GPU like this:
External (SB.PCI0, DeviceObj)
External (SB.PCI0.PEG0.PEGP, DeviceObj)
and your previous one addresses it like this:
External (SB.PCI0, DeviceObj)...
I use the same method to activate my R9 270 GPU, I don't use any bootflags so try removing these flags from the NVRAM section i the config:
After removing these flags reboot the system. reset the nvram and boot into macOS and see if anything changes.
Boot into macOS with the config that works; Use OpenCore Configurator to open the config.plist, navigate to Device Properties and remove all the items in the list and then add all your device properties form the list like shown in the picture.
Save the config and post it here so I can check the...
I know it's off topic but since people were asking for AppleIGB compatibility for Big Sur I just complied it for Big Sur for anyone who's interested so please test it and let me know if it works. I tested the kext on both Monterey and Big Sur and it seems to be working fine.
You are already in good hands with the help of @Edhawk but take a look at my EFI folder it might help you boot your hack, I have the same mainboard with a Ryzen 5900X CPU.
I'm use the same folder for Big Sur and Monterey.
Just give it a try and if it didn't work disable the SSDT-UIAC.aml under...