I was actually having a hard time finding this exact niche for a while, so I'm glad it's being asked. The hero's journey structure is so foundational, and seeing it applied to trans protagonists makes the whole 'finding your true self' arc resonate on another level. A book that absolutely nails this is 'The Unbroken' by C.L. Clark. It's not just a fantasy adventure; it's a brutally honest look at colonialism, loyalty, and physical strength, all through the eyes of a soldier who is a lesbian and, in my reading, carries a deeply transmasculine energy in her struggle for identity and autonomy against empire.
For a more classic, magical journey, 'The Bruising of Qilwa' by Naseem Jamnia is incredible. It follows a nonbinary refugee healer-mage who uncovers a mysterious plague. Their journey is less about slaying dragons and more about navigating systemic injustice, family secrets, and the moral weight of power—figuring out who they are in a world that constantly tries to define them. It’s a quieter, more introspective kind of heroism, but no less powerful for it.
I'd also toss in 'The Empress of Salt and Fortune' by Nghi Vo. While the central narrator is a nonbinary cleric, the story they uncover is about a deposed empress's legendary rise. It’s a masterclass in how to tell an epic, subversive hero’s tale through implication and recovered fragments, where identity and cunning are the ultimate weapons.