The general consensus seems to be that if you are a straight male before transition, you are likely to still prefer girls after. Of course, if you fully transition, and still date girls, that pretty much makes you a lesbian. If you were bi or gay before, even if you were hiding/repressing it, you probably still are, after transition.
In my own experience, I knew I was bi before transition, and generally preferred female partners. But by choice I stuck to girls, and repressed my attraction for some males. I was deeply in the closet, monogamous in a straight marriage for 30 years, had a kid, and was not even considering my feminine impulses impacting my reality until I was into my 50’s. I did not open up to exploring my gender identity or true sexuality until my parents and wife had all passed away.
When I started going out as a woman, that repression evaporated, and I felt much more comfortable accepting amorous attention from males (though I was always careful to make sure they accepted and understood that I was pre-op trans). What I found was that “men were okay, and definitely on the menu”, but that I still preferred women. I ended up socializing with a lot of lesbians, who saw the woman in me and accepted me as ‘one of them’ long before I was certain of my own transition becoming full time.
Today, legally female, 8 months into HRT and on track for full top and bottom medical transition, I remain much more open to dating women rather than men, but if the right man was interested in dating me, and fully accepted me, that would be fine. I consider myself primarily a lesbian woman, and am comfortable with the public seeing me as such.
