The config for this might come from a different package.
For example on KDE Neon it comes from neon-settings-2
Not really if your $SSH_ASKPASS_REQUIRE is set to refered (which I suspect is the case here)
From man 1 ssh
SSH_ASKPASS_REQUIRE Allows further control over the use of an askpass program. If this variable is set to “never” then ssh will never attempt to use one.
If it is set to “prefer”, then ssh will prefer to use the askpass program instead of the TTY when requesting passwords.
Finally, if the variable is set to “force”, then the askpass program will be used for all passphrase input regardless of whether DISPLAY is set.