it sounds as if the radio is not set to data mode. p.123 of the English user manual has instructions for setting up data modes. This applies to WSJTX, even though it's not specifically mentioned. The mode that you need is DATA-USB. If you're using USB for CAT control, then under WSJT-X, in Settings, and on the Radio tab, set Mode to Data/Pkt and that should change the audio source. The default appears to be None, which is probably not what you need.
Again, assuming that you're USB connected, then in the Audio tab select the FT-991A for Input and Output. [Not running Windows here, so can't provide specific details.]
HTH, 73, Stay Safe,
On 18/10/2021 03:47, Jay wrote: