All of the USB WiFi adapters I've tried work fine on a Windows 10 computer
Does the dongle work on this computer on another operating system?

Sorry, I don't mean to be boring, but to avoid comprehension problems and try to rule out all possibilities, I need more accurate information:
I want to know if this dongle ever worked ON THIS computer with another OS, and you claimed it works on ONE computer (doesn't make it clear that it's the same computer). We need to rule out a problem in THIS computer's BIOS, and/or some kind of specific conflict with this model, testing on another computer won't rule out this possibility, you know?

Cudy WU650

I don't know what the technical difference is or if there is a difference between drivers, but the version that is listed as compatible is the Cudy WU650S:

What are some of the other things I should try, before giving up and running a 75 ft Ethernet cable to the router?

Have you checked that there is no configuration to be done in the computer's BIOS?