Rockpro64 with 7i76e

yes (it can also be disabled in the interfaces file if you go that way)

Well I still can't ping it but at least I can now select it in the network manager.

But it doesn't stay selected.

I tried plugging it into a working router but still no yellow led on the 7i76e rRJ45.

100 BT router?

what is a 100 BT router?

Some hubs in older routers were 10 baseT only since the ADSL/Cable data rates were low

My router is Apple Airport Extreme. I also have an Apple Time Capsule.
I know the Extreme go 100mbit the Time Capsule supports gbit.
However, I didn't see the yellow led lit on any of the cables coming out of the Extreme.
They all have the green led lit.
Also the yellow led is lit coming out of the RockPro64 but not the 7i76e.