Linux Kernel v6.1.50, Desktop Sharing v23.8.1
I had the same problem and it turned out that the “Change Unattended Password” attempts to the change (Or perhaps actually does create a separate, different password) the password in the “Connection Settings” pane.
Result? If you change the unattended password so that it is different from the “main” password (A reasonable thing, to my mind), KRFB asks for permission on the host machine to allow the connection. If the unattended password is the same as the “Connection Settings” password, smooth sailing.