gender fluidity is playing pretend
you don't just out of the blue feel like a girl and then the next a boy and then a girl again
I mean, you don't have the kind of perspective to know that for certain.
When people tell me about lucid dreaming, there's always a part of my mind that wonders whether everyone who does lucid dreaming is just bullstuffting me. Like, surely after trying and failing at lucid dreaming for a few weeks, it must be pretty easy to just lie about it and tell your friends about all this cool stuff that never actually happened to you.
But since I've never had a lucid dream and I can't enter their minds, there's literally no way for me to have any degree of certainty about it. I think it's a good parallel for gender stuff, since most people have no personal experience with that kind of thing. It's your own prerogative whether you believe them or not, but you have to admit to yourself that you've got no evidence one way or the other.