Maybe 5 required fields and 30 optional fields. Apart from "census dweebs" [1] I don't know of many people that fill in more than the required.

[1]: https://thebeaverton.com/2026/05/local-nerd-disappointed-he-...

I'm not familiar with the specific example, but as a first hunch, if I had to implement such a system, it'd be part of the flow after the successful signup, not during.

You could also pretend to pass-through and watch the behavior of the "user" after success.