I’m not super up to date on Fluxer and how it works but I do know that they’re still working on getting full self hosting available. Without any other context, my assumption is that’s a requirement for their hosted instance for whatever reasons they have.

Besides, if it’s just asking for date of birth, is it really that much of an invasion of privacy? I mean the internet has been like that since the 90s and it’s been fine. You just lie if you want and the liability theoretically then moves to you instead of them.