Confirmed on the radio: it answers "?;" to KY, so this is not a setting to find.
My previous message sent the operator looking for a MENU → CW → PC KEYING entry I
named without checking it exists on that model, and they could not find it.
The message now names the path that does work: the "Serial port (DTR=CW /
RTS=PTT)" keyer on the rig's OTHER COM port — the standard one — while CAT keeps
the enhanced one. Same for the settings hint and the changelog.
The KY engine stays: it is documented for the FTDX101 / FT-991A / FT-710 family.
It now fails loudly and usefully on the models that lack it, which is the
difference between a dead feature and a wrong one.