Big Sur and other MacOS versions include a driver from Apple that has known conflicts with the FTDI driver used by Ruida. The telltale is that you get exactly one use, then the port locks out, and you have to reboot to use it again.
There’s a newer driver at the bottom of this thread:
That one has reportedly fixed it for a few people, but if it doesn’t work for you, there are a few other options above that post in the same thread you can try. They involve varying amounts of fussing on the command line, so we generally suggest an Ethernet cable instead, but try the driver first and let us know if that helps you.