This Default Field Type is available in Profile Builder 2.0 free version.
The Default – Display name publicly as field only appears on the Edit Profile Page. Inside the field options you can set the field title, description and default value. Also you can set it be Required or not.
Users can use this field to set up their display name to: nickname, username, first name, last name, first name last name, last name first name.
This is how the Default – Display name publicly as field we created above looks like in the Edit Profile page in front-end.