OK, everybody, this is a nuclear bomb. Get to work solving my problem or we all go boom! NOW!
Heheh.
I was afraid that would be the answer. I can confirm that the "Platinum - USB-C to Ethernet Adapter" from Best Buy works like a charm with Unraid. $20.00 USD. (This motherboard has 3 PCIe slots and I have all three filled, 2 with LSI 9211s and the last with a graphics card.)
I'll mark as solved, pending kernel 5.15.