I would probably call them 'boards'. Communities is too long of a word imo and it makes it sound like the people subscribed all have some kind of shared culture or relationship. That definitely happens in some cases (there are subreddits which have built a community around them) but it's not universal.

I'm trying to think of questions that have a similar vibe. these may be way off (I'm not trans) so take with a grain of salt -

a religious person meets someone in their congregation and asks if they are a convert or were born in.
a person on a date asks their date, a single person, if they are divorced or never married.

I think I would struggle to define the category being asked about in these questions too. It's something about history and expectations.

You might call the category lived experience. Does your gender identity match your lived experience and upbringing, or does it not? Sometimes you see trans people use the phrase 'man of trans experience' or 'woman of trans experience' to highlight that the word trans applies to history and experience. So the question might be, "what is your gender experience?" or "what is the nature of your gender socialization?"