It's very funny that Hemingway has the reputation of being a man's man bro misogynist writer, when actually he was a fancy lad who was always in crisis about his own masculinity.
Also, read his final, posthumously published book, The Garden of Eden if you want some good gender stuff. It's about a couple on their honeymoon that start dressing androgenously and trying to become the same person, and it's very strongly implied that the guy is getting pegged by his wife. It caused a major critical reappraisal of Hemingway when it was published
Before we start: I am using the term "transgender" in its most common meaning here, i.e. as an umbrella term for all kinds of gender variance.
I agree if we're going with the broad definition above. Certainly there was GENDER stuff going on with him, but it's kind of hard to pin it down more specifically than that
having consumed a lot of fanfiction over the years, you tend to notice what the kinks are for each writer. some of them try to hide it a bit more but others will just bulldoze straight through a wall with pet-play in the second chapter*
*this obviously excludes the "porn what plot?" -fics