Ethernet not working after update from Catalina to Big Sur

Hi group.

I just installed Catalina from scratch, and it was working fine, but then I immediately updated to Big Sur (through the normal update process), and now I have no ethernet. Any idea what might have gone wrong, or how I can debug this?

My hardware: i9 9900K, XFX RX580, 32GB, Z390 Aorus Pro Wifi. I followed the main OpenCore install guide (https://dortania.github.io/OpenCore-Install-Guide/). I am using the debug OpenCore version, enabled verbose output, but I see no error/warning regarding IntelMausi.

While the problem is related to Ethernet, I also tried the AirportItlwm / IntelBluetoothFirmware drivers in case I could get the motherboard internal WIFI to work, but no luck on either Catalina or Big Sur. So, I have disabled them in config.plist.

I have googled about this, and tried all possible BIOS settings, with no change. Not sure how to debug it or what to try. I would appreciate any ideas.

Thanks!