thank you for engaging with the question. Building on that, my point is that it is clearly somewhat arbitrary where you draw that line - you could in theory have sex with a trans man (assuming it didn’t involve their genitals) without having any reason to know they were trans (and acknowledging the potential legal issues - although the case law suggests it’s probably only an offence if they intentionally deceived you - and not that I’m saying it’s therefore ok, as no one should take risks about another person’s consent).
Clearly many people, like you, will stop finding a person attractive if they don’t have the genitals they expect - either because the genitals themselves are unappealing to them, or because it means they can’t have the kind of sex they would want to have, or because it reveals to them that the person’s biological sex is not what they believed it to be, and that changes how they see the person more broadly.
but there are other people for whom other aspects of a person’s physiology are just as - or more - important. I was chatting to a colleague who’s a gay man in the pub the other day, and we were discussing the nature of sexuality. I was saying how, as a bisexual, I find it hard to imagine how straight or gay people can know they will never, in the whole course of their life, fall for someone of the same/opposite sex. He was saying that his identity as a gay man is important to him, and part of that is the ability to say he will never find a woman sexually attractive, and for that to be believed. But he also said that he could find trans men attractive, because what is attractive to him about men does not hinge on genitals - it’s things like the hairy body and face, the six pack, deep voice.
Wouldn’t it make more sense, rather than trying to pin down and set in stone the boundaries of different categories of sexuality, to focus on what’s important - that no one should ever be pressured to have sex with anyone they don’t want to, and they don’t have to justify why they don’t want to. I hope everyone here would agree that a straight woman or bisexual should never be made to feel bad because she doesn’t want to have sex with (or kiss, or go on a date with) any particular man, regardless of the fact that she chooses to do those things with some men?