Because you say you’re more feminine, I wonder if it’s western society’s image of a “man” that you don’t like. I’ve been into transgirls since high school, but back then they had to be cis passing. Now that I’m 30 I’m less picky, and I’m even starting to like some guys with facial hair. There is something to be said for novelty, and if you’ve never tried a partner with a dick, how do you know you won’t like it?
Naw, I’m just not into anyone with male genitalia at all, even if everything else presents as feminine. To be entirely honest, I’m not sure where “the line” of attraction is for me, since I realize there are a lot of factors at play here, but I imagine it would be decidedly on the feminine side overall.
As for how I know I wouldn’t like it, I guess it’s like an aversion to something like a food? I just see it and think “no thanks” lol. You’re right that I may never truly know, but I’m reasonably confident.