A Google search shows how tricky it can be to get an X570 Aorus motherboard to correclty detect your GPU, especially if you're already using one of the PCIe slots for a GPU + another M2 PCIe slot for an NVMe SSD, which was the case for my build.
Therefore, neither my BIOS nor my OS detected the 2nd GPU card right away. I spent some time reading the motherboard manual, but nothing there was immediately helpful. The section on PCIe did mention how to split the available lanes in case multiple were being used for PCIe Gen 4.0 devices (which by default will use x16 lanes), and that's what we rely on here via the "bifurcation" BIOS feature listed below.
I got it to work successfully, so sharing it here in case somebody out there finds this useful.
Assumptions: