If you're interested in trans history, I have a ton of recommendations.

Gay Berlin: Birthplace of a Modern Identity by Robert Beachy is mostly focused on gay men, but there's a lot of good material in there about trans people in Germany in the early 1900s until the seizure of power by the Nazis, including how trans people interacted with the state, the early days of the Institute for Sexual Science (the world's first queer clinic), and other good tidbits. There's a fair amount of pictures in the middle of the book, though again mostly focused on the experience of gay men.

The Hirschfeld Archives: Violence, Death, and Modern Queer Culture by Heike Bauer has more of a focus on Magnus Hirschfeld, the founding sexologist of the Institute for Sexual Science, and how the Institute functioned, and its eventual tragic fate under the Nazis. There's a lot more in here about trans people in particular than Gay Berlin, but both are good reads. A fair amount of pictures in this one as well which are really interesting. Seeing inside the Institute is really fascinating.

Discretion and Indiscretion by sexologist Ludwig Levy-Lenz are the memoirs of the head gynecologist at the Institute. Written in Egypt in the 1940s or so where he settled after being exiled from Germany for being both jewish and being involved with the Institute, much of it focuses on his life before he met Hirschfeld, though it's worth reading if you find 20th century sexology interesting. However, roughly the latter quarter of the book is related to his time there and it is an absolutely captivating read, including my favorite quote of all time, "I performed these operations [hair removal, orchiectomies, vaginoplasties] at the Institute—they were reported at the time in the daily press—and I did in fact succeed in forming an organ resembling the vagina—never have I operated upon more grateful patients." Do be warned though that he will just random go off on weird eugenic tangents. It's a wild ride.

The Institute of Sexual Science: The Only Institution of its Kind in the World by urologist William J. Robinson in his medical journal The Medical Critic and Guide is a really interesting look inside the Institute when he visited in 1925. It can be found here: https://hdl.handle.net/2027/mdp.39015011423632 on pages 391-396 (which correspond to 397-402 in the viewer). It's a short read but it includes a very funny scathing condemnation of the puritanical culture of the United States, where he laments he would never be allowed to open an analogous clinic State-side. While he has good intentions, he calls literally every queer person he sees in the Institute a "homosexual," but it's easy to read from the context that a lot of the time he's actually talking about trans people.

Unfortunately I have not read much of these two following books, but I have listened to the author's lectures a few times and he is very good. Laurie Marhoefer's Sex and the Weimar Republic: German Homosexual Emancipation and the Rise of the Nazis and Racism and the Making of Gay Rights: A Sexologist, His Student, and the Empire of Queer Love are solid sources for this period of queer history.

If you're interested in more primary source stuff, Michael Lombardi-Nash from Urania Manuscripts has been translating Magnus Hirschfeld's publications into English if you can't read German.

As far as "theory-adjacent", for lack of a better phrase, goes, I found Program for a Transgender Existentialism by Penelope Haulotte in an issue of Transgender Studies Quarterly a few years ago to be a very thought provoking read. I've been meaning to make a post about it but I am perpetually lazy I guess. You can find the journal pre-proof here: https://philarchive.org/archive/HAUPFA, which as far as I can tell is identical to the copy that made it to print.

For slightly more modern history, Jules-Gill Peterson has an excellent, if harrowing, book called Histories of the Transgender Child, which covers how intersex children were brutally experimented on in the United States and the doctors who did so invented the concept of gender to prevent the obvious conclusion one could draw from their work that sex is not binary at all and is actually quite plastic and can be modified if one wishes with the right inputs. Further, that sex is not determined by a single aspect, but rather is a messy amalgamation of a number of traits and systems within the body. She also attempts the difficult task of reading trans children in the archive, showing that trans childhoods did take place even at great distance or total isolation from the medical system.

If you have an interest in ancient history, then I have a couple more:

The earliest non-anonymous writer in the entire historical record was a woman named Enheduanna. She was the High Priestess of the Sumerian moon god Nanna, but her personal deity was the Sumerian goddess of love, sexuality, war, and political power, Inana (alternatively spelled Inanna, and known to the Akkadians as Ishtar). She wrote a series of poems about Inana which contain very explicit mentions of people who transgress gender boundaries and take up new gender identities. To keep my comment here ~~brief~~ less of a wall of text, I'll link one of my previous comment about these poems here: https://hexbear.net/post/4139599/5757960, which include relevant quotes from the poems. You can find these poems in Inanna, Lady of Largest Heart: Poems of the Sumerian High Priestess Enheduanna by Betty De Shong Meador.

For a broader perspective on queerness in ancient religions, Blossom of Bone: Reclaiming the Connections between Homoeroticism and the Sacred by Randy P. Conner is a great source. Despite the subtitle, there is a decent amount of people you could very broadly descibe as transgender, in that they transgress their societies gender boundaries, in the book. It covers a wide range of cultures and time periods.

Most of these books can be found on Anna's Archive. Levy-Lenz's memoirs I don't believe are on there and are unfortunately a little expensive because it has been long out of print and now exists solely as a print-on-demand book unless you drop an eye watering amount of money on an original copy.