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.