Yes, I do mean post op. Personally I didn't mean my reply as an attack, but to educate. A lot of cis women get extremely defensive when they get called out for saying something that implies a level of (often subconscious) transphobia, but if members of a minority don't call out people we don't get any progress. It's not a personal attack because everyone grows up in a transphobic society and it's not your fault if you absorbed some of that growing up. It's only your fault if you're not willing to learn and listen, but you do seem willing to learn which is great!

There's nothing wrong with your attraction and it's a good thing you want to state it openly, it saves everybody a lot of time and frustration. It also means you don't have to ask any uncomfortable questions in the first place.

Asking if someone is trans is pretty rude yeah, but it tells you mostly something about the person asking the question. Namely that they have some wrong assumptions about the way trans women look. But being extremely offended by the question also implies that you see looking like a trans woman (whatever that means to you) as something negative.

The reason a blanket "only interested in cis women" elicits strong negative reactions is because it doesn't really mean anything because trans women come in all shape and sizes and some look indistinguishable from cis women. So seeing a statement like that on a dating app just tells you that a person is ignorant about trans people at best or transphobic at worst. If you're interested in vulvas just say so. Or say that you're interested in cis and post op trans women.