I have an older ASRock Rack motherboard, and I also had my share of struggles with their BMC port sharing. On this motherboard, from what I found in my research, this virtual AMD port appears when instead of using a dedicated BMC port, you share this port for other purposes, or when you only have one cable connected to a certain port.
As far as I understand and remember, the settings for this behavior are not in the BIOS but in the BMC’s web interface. In the Configuration section, there should be several options for network, link configuration, and choosing between shared or dedicated. One of these options should disable this virtual interface, but I’m not entirely sure. The motherboard manual might provide more detailed descriptions of the BMC settings, but on my board, these settings are quite confusing, and the manual doesn’t cover all of them.
Overall, I had a similar idea—to have access to both the BIOS and everything else. But as usual, since their BMC relies on Java, which can’t be updated, it’s impossible to use their applets because the board is no longer supported. In the end, I connected a PiKVM to this board.
For anyone considering purchasing an ASRock Rack, I highly advise against it if you plan to use the board longer than its support period (typically 2-3 years), as the BMC might "turn into a pumpkin" after that.