Jules Gill-Peterson has a recent academic book, Histories of the Transgender Child, that covers the early- and mid-20th century. I wrote about it briefly here: https://tuckerlieberman.medium.com/historical-transgender-children-ff239a515d51

Susan Stryker's Transgender History (2009) begins with the WWII era. I haven't read it yet. She has newer books and articles, too. Two days ago, she gave a virtual talk through a historical society. https://bookshop.org/a/4480/9781580056892

I would be remiss if I didn't mention that my own book, Ten Past Noon, is a biography of a New Yorker in the 1930s who read everything he could find about castration. The second of my book's three sections, especially, is about this moment in history when it was hard to find printed material on the topics we'd now call unambiguously trans, and why this man in particular struggled to find what he was looking for. https://tuckerlieberman.com/ten-past-noon/