Link below very useful for getting FT991 to run on Macbook with a single USB cable.
(Above site has detailed instructions and system worked fine on Oct 24, 2021.)
Another Set Up page for FT-991 to Run WSJT-x is at
This is very different from first link, but still very helpful.
WORKS if Mode on radio menu is set at DATA and other right hand choices are RIG and HARDWARE NO POWER OUT, HOWEVER
Need to check Transceiver is set to USB-Data
If not working, check that the SiLabs driver assignment is right one.
There are several in the small menu window.
Monterey still needs a driver downloaded from SiLabs.
Monterey has inadequate timing accuracy for wsjtx to work reliably. I dealt with this via a computer clock setting app .... ChronyControl... recommended by a member of the wsjt discussion group. ChronyControl gives excellent timing accuracy and allowed WSJT-x to work on Mac Monterey.