Can a 10Gbps USB 3 host controller be configured to work at 5Gbps?

Oh yes, X would be AMD fixing their defective USB controllers but that won't happen on a system produced years ago. 😂

Great question. In short, garbagy AMD USB controllers. I recently switched to a newer AMD board and have been hit with the same issues faced by these poor sods. I've been conducting testing over the last week, different combinations of ports, cables, loads, add-in PCIe USB controllers. The add-in cards seem to behave well, which is one way the folks from that thread solved their problems. The other being changing to Intel-based systems. Yesterday however I was watching an intro about USB redrivers by TI and they were discussing various signalling issues that could occur and how redrivers help. That led me to form the hypothesis that what I'm experiencing might be signalling related. E.g. that the combination of controllers/ports/cables simply can't handle 10Gbps. That might be noise from some of those devices or surrounding ones that causes signal loss when operating at 10Gbps, speeds this setup can actually achieve. In order to test that I tried placing the DAS boxes behind a 5Gb hub plugged in a port that has previously shown a failure. So far it's stable. This is why I was wondering whether there's some magic in the kernel that could allow configuring 10Gb ports to operate at 5Gb.

Already done. I'm just trying to exhaust all the hypotheses I have in case I stumble upon a durable workaround that is applicable for others and cheaper. Good USB add-in cards are not cheap.

Probably a USB controller, considering that is what they said explicitly in the title. And probably the bandwidth the controller advertises to downstream devices.