I tried to follow your reply but I don't see a few of the settings in my Bios: 4G Decoding, SecureBoot, FastBoot, nor how do I know if I need iMacPro1,1 or Macpro7,1?
I wish there was a flow chart for "AMD & B550-A pro" w/ default settings to get the MacOS installed THEN deal with the kexts one...