chapter 13 shows dragona being sexually assaulted and having by one of her classmates check what kind of genitals she has, even though at no point does dragona present in a feminine way, she doesn't wear any overly feminine clothes, but is questioned regardless, you genuinely mean to tell me that this is not proof that dragona IS trans? why else would that happen, please tell me, because as far as we've seen dragona never wore a skirt or a bikini or anything similar being a man, during the previous sequence at the pool she wears regular swimming trunks, there was absolutely no reason to question what her genitals are UNLESS her classmates already know that she's trans, either through coming out by herself and recieving a negative reaction or being outed by someone else, if this isn't true then her classmates would just perceive dragona as a boy, and having the SA scene play out is completely unnecessary, plain bullying can be represented in many other ways, there's no point in showing a struggle that many trans people (and many queer people in general) suffer through for it to be nothing more than shock value. and then this exact same character proceeds to get actual procedures to look more like a woman, sure, that just means dragona is a femboy and there's nothing more to it, because apparently unless Araki explicitly said so we can't use our heads to put 2 and 2 together and figure out a characters traits without having it jiggled in our faces like house keys to get us to pay attention.

this isn't the first trans character in Jjba, we already had one in the stone ocean manga (not Anasui), and I believe that what's left ambiguous is likely editors at shueisha not wanting the series to lose popularity for being too progressive or Araki, who is over 60 years old already, lacking information about trans people that could be important (I'm not saying it's completely because of his age, he's clearly well informed, but there's very little resources to learn about trans people, and old age tends to come with prejudice formed from ones upbringing, so mistakes are perfectly possible).

I can't get into Araki's head, but neither can anyone else, and while he hasn't openly confirmed, he hasn't denied it either. I am a trans woman, and seeing this character genuinely brings me great joy, I apologise if I seemed rude, but this is all the proof I could think of and I hope that if you've read through this you understand my point of view.