Kind of amazing that a macbook pro has four 40 Gb/s ports... and none of them are ethernet. Compare to 1 Gb/s ethernet which was rapidly adopted by Apple laptops as well as desktops. (Though you can currently get a Mac mini (!) with 10 Gb/s ethernet built in - if you can find something to connect it to.)
I've used thunderbolt cables to connect laptops together for fast data transfer. I think in order to get decent performance I had to get disable the software ethernet bridge.
Those are Ethernet ports, just SFP+ ports rather than the RJ45 copper you're probably used to. I've never seen RJ45 ports > 10Gbps. Even 10Gbps is more often than not SFP+. Even if Cat8 can theoretically can 40Gbps, it wouldn't really make sense to put copper for those speeds today IMO.
This device looks to be target for network engineers, who can use it for testing and benchmarking infrastructure, or for installations that will most likely be in or next to racks rather than on desktops.
You could just pop a transceiver module that will convert the port to RJ45. The price of those is peanuts compared to the 2k list price of this device, and the reverse isn't viable.
IIRC each side of the macbook pro only has a single Thunderbolt controller. So it's actually 2x 2 ports sharing 40Gb/s. If you need more than 40Gb/s, for say dual external gpus, you'd need to use cables on opposite sides.
I've used thunderbolt cables to connect laptops together for fast data transfer. I think in order to get decent performance I had to get disable the software ethernet bridge.