Yes, the hormonal imbalance theory. I believe that is a prime cause of much homosexuality. Highly muscular lesbians dominating female sports promotes that line of thought.
I just read a biography of Montgomery Clift. He was a paternal twin, the other of which was his sister. The biography said that multiple times in his life he wasn’t sure whether he was a boy or a girl. I wonder if a boy being a paternal twin with a girl has greater odds of being homosexual? (I have no opinion one way or the other. Just wonder.)