Quick orientation before you press the button:
Wizarr may start with a Plex sign-in because Plex has its own invite handshake. That is normal. Keep going: this invite is already connected to the other media libraries too.
If you actually need the big family app account for photos, files, notes, planning, and dashboards, use Authentik instead at auth.rasies.com. This page is the media lane. :)