I'm not familiar with much trans-specific content on GA, although there's plenty of genre-fiction to be found here across the entire hard-SF to high fantasy spectrum. I can speak to a few standouts in the SFF literary canon, though. If you are already familiar with any of the titles or series below, I'd love to know what you think of them and I can perhaps recommend other stuff specifically. Here goes:
Ursula Le Guin's The Left Hand of Darkness is definitely the first thing that comes to mind. I remember being absolutely floored by that novel in highschool (it was the early 90s and there just wasn't TransANYTHING to speak of). I kept giving it to all my friends and trying to explain how they needed to understand the Gethenians in order to understand me. The world of that story, Gethen, is inhabited by people whose sex, apart from social constructions of gender, is changeable from a sort of default "neutral" to poles of male and female that manifest according to their biological/reproductive cycles. There is a human male narrator -- an alien in the Gethenian world -- who functions as a foil for the Gethenian characters, and an avatar for the reader. The linked review gives an excellent and concise discussion of the literary merits, which I have not really attended to here. Le Guin wrote this story in the 1960s and at the time it was a pretty groundbreaking examination and reflection upon sex and gender in society.
Also firmly in the SF category (practically space-opera, sometimes time-of-war) are Iain M. Banks' Culture novels (not to be confused with Iain Banks, who is the same author in his non-SF persona). The humans -- or should I say post-humans -- of Culture worlds live in a society that preserves the basic constructions of sex and gender with which a contemporary Western reader would be familiar, but the future utopia is post-sexist, non-misogynistic, and generally entirely sexually liberated. The personal naming conventions used are sufficiently exotic that I have often been unsure of whether a given character is intended to be male or female until specific physical description is given. Not that this really matters, though, since bioengineering has given people the ability to change sex at will throughout their much-extended (centuries-long) lives. While this ability has not featured prominently in the plot of any of the Culture books I have read, it has definitely been mentioned in more than one novel and had some contextual significance for several characters. For bonus fun, the sentient starships -- colorfully self-named AIs, who are pretty clearly the ones really in charge of Culture society -- are tremendously entertaining characters in their own rights, and I have often found myself most looking forward to what the Steely Glint, the Fate Amenable to Change, the Problem Child, the Appeal to Reason, or the Grey Area (aka Meatfucker) would contribute to any conversation. Banks passed away a few years ago, shortly before the publication of his final Culture novel. Most of his work is now being reprinted and should be easy to find. While it is not necessary to read Culture books in order, there is some historical continuity. The first chronologically is Consider Phlebas.
Though I would not specifically call it SF or fantasy, I highly recommend Ali Smith's Girl Meets Boy, a contemporary retelling of the story of Iphis from Ovid's Metamorphoses. This myth is specifically a story of gender ambiguity and transition, and reads strikingly modern even in its original telling from 2000 years ago. Smith's rendering, published in 2007, is quite fun, and while Iphis' story is a transmasculine narrative on the surface, even Ovid's original was a recognition of the flexibility and adaptability of people and society (with the aid and blessing of the gods.) Smith does not treat it solely as a story of binary gender transition. Her version is a fast read, but many-layered, and I should probably give it another look myself.
Finally, I should mention the James Tiptree award on general principle. James Tiptree, Jr. was the penname of mid-20th century SF writer Alice B. Sheldon. The Tiptree award is "an annual literary prize for science fiction or fantasy that expands or explores our understanding of gender." Unfortunately, the organization's website (linked above) is pretty shit, but the writers they recognize and those that serve as jurors and organizers are top-tier. I am certain you will find characters and stories that speak to trans experience among Tiptree honorees.
I DEFINITELY read my share of cyberpunk back in the late 80s/early 90s, and Bruce Sterling, Rudy Rucker, and Neal Stephenson are some of my very favorite authors of this SF vein. I cannot recall any trans-relevant stories, characters or themes from their work that I have read. However, I do think there's some interesting ground to be mined as to the appeal of cyberpunk worldview(s) for trans, GNC and nonbinary-identifying readers -- but this is already crazy long, so I'm happy to pursue that conversation another time, if you care to do so.
So, be welcome to GA -- I'm sure you will find plenty of good reads here . And I hope that the information above is of some aid or interest to you as well. Feel free to hit me up anytime if you want to talk more about this stuff, or about other good reads (even non-SF!) on and off this site. My real wheelhouse is music and music history -- but if I don't know a thing I might want to learn it. I can at least try to point in the right direction, or boost a signal to someone else who may have the perfect answer.