The registration builder have been moved! From project settings into the registration module within the timeline on the intro slot (before called auth). To convert an already existing project into the new registration functionality you just have to open the auth/registrationmodule.
In project settings you will now find “participant fields”. Participant fields are fields connected to the user but not a part of the registration. For example groupings and other info that you as an organizer have but that you don’t need from the participant.