If it doesn't, choose the other or closest option. It's unlikely there isn't one.
> there are places where IDs allow for more than those two options.
Sure, like here in NYC. That's really more of a personality thing IMO, which gets conflated with sex. Wherever necessary, things still reduce down to a binary choice, with the rest being details.
You likely still identify as masc or femme in some sense, so chose the closest option.
My point is simply that there is likely a 'closest option'. Obviously people don't have to use any service they feel doesn't cater to them, but when a service doesn't always offer more than the binary it doesn't have to always be a "woe is me, how could I ever proceed" scenario.
The site seems to be a kind of dating/singles chat, if that's the case having genders/sexes makes some sense, although indeed it could be better.