The problem with my build (see my signature) is USB mouse and keyboard actually works fine. Besides that, the front USB 3.0 port seemed to run at USB 2.0 speed and all back USB 3.0 ports did not work at all.
So basically I followed Norton's solution: a) install GenericUSBXHCI.kext using Kext Utility, and b) copy it to EFI/Clover/Other
All USB ports seem to run at USB 3.0 speed. (I used "seem" because I didn't run a formal test but just eyeballed the rate while transferring a reasonably large file)
I wished I knew before this
Kext Utility, although on its website, says it only supports up to Sierra, it works fine with High Sierra.
In the system report, the USB section still shows "no information" but I don't care.
ASRock AB350M Pro4
MSI GeForce GTX 1080 Ti DirectX 12 GeForce GTX 1080 Ti GAMING X 11G
ADATA XPG GAMMIX D10 16GB (2 x 8GB)
Crucial MX300 525GB