Well if you actually did at least one google search, you might have found out that both body dysmorphia and gender dysphoria are two different mental disorders.
Yes, gender dysphoria is classified as a mental disorder, and guess what's the treatment? Gender affirming care - because people who actually specialize in this topic and spent years studying it realize that it's real.
As for your advice about reading books, I doubt you'd actually let facts interfere with your desire to insult people but for starters, i recommend this article:

https://www.sciencedaily.com/releases/2018/05/180524112351.htm