I agree except gender can be a very uncertain, iffy topic. it's folly to assume that everyone is able to describe exactly how they think about it, or to think that OP necessarily can answer this kind of question. especially as they repeated in their post that they don't care.

I'm allowed to not care about my gender. and if somebody thinks that I need to define it in order to marry them, then maybe they shouldn't marry me. you can't force me to do that kind of mental labor, just like fiance can't force OP to just because she wants to know. it could realistically take decades for OP to really understand, especially if they haven't even really begun exploring it.

there's a difference between hiding it and not knowing. it sounds more like OP is exploring, doesn't know a concrete answer and can't give one... less like they are lying on purpose.

people "hide" shit from other people all the time, stuff that they're not certain about and don't know how to to express. there is no rule that says your relationship will fall apart if you cannot express literally everything. if that were true, no one would be in a successful relationship. sometimes it takes people time to be able to articulate this kind of thing.

so while I agree that OP should be communicating with their fiance, that doesn't mean that they know exactly what to say. fiance took a big step assuming that OP was "transitioning," likely because they read about it and are trying to understand it. their heart is in a good place! but sometimes you just have to accept that people don't know the answer every time, that maybe they have a partial answer that they don't want to give because you will assume that means something. it's not bad to want to protect part of yourself until you get it yourself.

God, if I had to share my in progress thoughts with everyone, no one would understand me. they would get this half formed idea of me because that's what I told them and that's what they know. it's hard to communicate with people who want to know the answer, if you don't know the answer. this is a delicate situation. your comment is very black and white and doesn't apply.