It is not possible to choose Left or Right audio channel in 2.3.0. and 2.4.0 rc1.
Both audio channels have the same content.
Using USB audio input.
Other applications have no difficulty using the same L/R USB microphone input.
They see a clear difference between L and R input (and can select one)
Mic. is set fot 2 channel, 16 bit, 48000 Hz. (but other 2 channel settings make no difference)
Did try other USB ports of the PC.
I deleted all WSJT instances, cleaned the register, removed all USB audio ports (hidden and shown), restarted several times.
Did a new install on a separate laptop.
All with no result.