I think I've really messed this one up. I have Debian 10 (Buster), WSJT-X 2.2.2 compiled from sources, USB comms with CAT control. Fldigi is NOT loaded or needed.
Previously, I had version 2.2.2 working very well with Ubuntu 18.04 but other OS problems forced me to do a re-install. After Boot-n-nuking the disk to all zeros I installed Debian.
Somehow I got the impression that hamlib was needed to do CAT control but I think that was erroneous thinking on my part. I downloaded and compiled hamlib and compiled WSJT-X against hamlib.
Now I'm getting protocol errors when I attempt to configure WSJT-X for CAT control on /dev/ttyUSB0.
I created a group called wheel to which myself and root are a member as well as the USB ports. I'm also a member of tty and dialout groups.
I would like to get back to the installation I had with Ubuntu (which worked great for over a year) in which JS8Call, Qsstv and WSJT-X all ran (not at the same time of course) great connected directly to the USB port with CAT control.