Comment by mcoliver
3 years ago
Re speed, looks like the cables are the right ones. Would be nice to find a wiring diagram of the motherboard to see how the pcie lanes are allocated but hard to find on these consumer devices. Perhaps each usb4 port is a single lane gen2 which would top out around 10Gbps. You could try paralleling iperf3 to give you a bit more info. Also check the tx_speed and rx_speed in /sys/bus/thunderbolt/devices to see what it is negotiating.
Company specific TB driver/firmware updates can be found here https://www.thunderbolttechnology.net/updates
I believe you might be right regarding the port itself being the issue here. I have a Minisforum UM775 (basically the previous gen of the 790 Pro mentioned in the OP) and despite having two "USB4" ports, only one is rated for 40Gbps while the second one is 10Gbps.
I cannot find any specifics regarding the ports on this 790 Pro one, but I'm certain that's ultimately the issue: the bottleneck is on that second (the one on the right) USB4 port.