I seem to have encountered another bug when comparing my two X470D4Us:
The proper way to remove the Intel I210 from being able to access the BMC is to first deactivate its bonding in the network settings:
Open Network Bond Configuration and disable the checkbox:
Then you can go into Network IP settings, select eth1 (the Intel I210 NIC next to the VGA port) and deactivate it:
Now there’s the issue:
My two X470D4U units have the same BIOS and BMC version (L3.25/1.90) but one motherboard doesn’t show the option Network Bond Configuration.
Reflashed both images and reset the firmware to factory defaults on the one not showing the option, but no change there.
Do you have the Network Bond Configuration option?