Trying to configure the IIS probe using windows authentication on the localhost does not allow to press the test button, it is greyed out.
Localhost is not supported as the hostname when configuring Windows Authentication in the IIS probe.
Any IIS probe version
If you change the hostname entry to the local short hostname, the test button becomes available. In order to have windows authentication enabled and able to test this, you need to treat the webserver as a remote server and provide the hostname or IP address in the hostname field of the profile.