I am 100% sure, that a B550 Board does not need an extra kext to get Ethernet working with iMessages/iCloud.   As ghost82 already mentioned I would try the following steps: 1) Setup propper XML with the right bios OVMF and Q35 for mac OS. 2) Setup network to <model type='e1000-82545em'/> 3) Setup propper SMBios with a non registered Serial, etc. 4) Delete network kexts in   /Library/Preferences/SystemConfiguration/NetworkInterfaces.plist /Library/Preference