Motorola MB8611 not Showing 2.5 GB Connection

My equipment is as follows:

Modem: Motorola MB8611 (brand new)

Router: Asus RT-AX86U AX5700 (brand new)

Motherboard NIC: Realtek PCIe 2.5GbE Family Controller (Asus ROG CROSSHAIR VIII DARK HERO)

The modem is plugged into the blue connector WAN on the router and the PC is plugged into the green LAN 2.5 connector. I have 1.2 GB service but the blue light (indicating 2.5 GB) on the modem remains green. I note that when I plug it into the 2.5 port on the router that the light turns blue. But, then, do I plug the PC into one of the yellow ports? When I do that, WIndows shows that the NIC is now operation at 1.0 instead of 2.5.

The bottom line is that, no matter what combination of connections I use, 960 GB is the best that I get. I'd be happy with that if I knew that had all of the wiring correct.  I am using Cat 6 cables.

Is there something else that I can try?