Of course you would think that trans people have never existed in schools when most students, teachers, and administrators would have treated them with absolute ostracism, at best, until fairly recently. But a 45-year-old trans woman was a 15-year-old trans girl 30 years ago, and many of them even realized it then, at least to some extent. Even for children being openly trans, it's been longer than you think, but people who have been out of school for decades (for which I'm very thankful) always have an outdated image of what it's like.
Your claim that "no one had a problem with dressing up as a woman" is a transparent lie to anyone with any sense of history.
By the way, we agree that gender dysphoria is best treated with therapy and drugs.
We just don't agree on what those consist of.