Remove support for mmconfig config space access in the kernel configuration, it’s broken on Asus boards with recent kernels apparently (I have this board, and nothing that’s connected on PCI works with mmconfig enabled). It’s here in the kernel configuration:
Bus options (PCI etc.) —>
[ ] Support mmconfig PCI config space access
You can also boot with “pci=nommconf” added to the kernel parameters, it should disable mmconfig too.