yayyyyy thank you!!! one of my favorite aus. :) heres some more fun tidbits for you about it:

steve was initially a nurse during the war & she gets updated emergency medical training in the modern day, but nobody remembers this about her bc it doesn't fit the "Captain America" image.

bucky post-ws really prefers nobody knowing anything about him even a little bit, so he obfuscates his own gender as much as possible. his gender situation is genuinely 'straight cis man from the 1940s' but he is trying to hide it anyways.

he also worries about steve's safety "as a woman" specifically, so he never corrects anyone who gets her gender wrong. they don't need to know that. why would anybody need to know that. he uses he/him pronouns for steve in the field because of this, and because they had to do that during WW2 and his memory while in active battle isn't the best. ultimately this means natasha feels really vindicated in her reading of steve's gender bc bucky appears to be following the same rules (he/him as captain, she/her in private) for steve.

bucky always uses he/him pronouns for steve in front of tony, even if it's non-hero private events like birthday parties or checkups on his arm.