Use Outlook and GPGOL to send a signed email message.
Kleopatra shows the "Select Certificate For Message "<Subject>" - Kleopatra" dialog, showing exactly one available OpenPGP certificate and no available S/MIME certificates.
Expected behavior is that the selection dialog will not be shown.
In Settings -> Kleopatra -> Crypto Operations, the option "Don't confirm signing certificate if there is only one valid certificate for the identity" is checked.
Also attempted to check "Only show this dialog in case of conflicts (experimental)", which did not change the behavior. That checkbox remains checked on the next attempt, and the dialog still shows.