I personally don't think it matters much at all, except in channels that specifically identify that way. However, I am male, hetero, cis, so its possible I'm just clueless.
Why not make a new account with a femme sounding username and see? Don’t pretend you need help with a bra or anything, just interact with lemmy while “labeled” a woman.
I have a more masculine username and a more feminine username (both seem like spins on given names, think UrArthUr and Bekky), and there is a difference in how I’m perceived, or at least how people respond to me. It’s not huge, and I’m afab irl, so I’m also not surprised- I don’t think I’ve ever
been somewhere where people can freely interact and it had no effect (or at least not since I grew tits).
There’s always a difference in how men and women are treated. It’s not always a horrible evil sexist thing, but people pick up on cues from tone and username and react to that.
Being online is nice, because the default assumption is that you’re a man, so unless you have a super femme username or are talking about something femme-coded like gardening or knitting, people tend not to treat you like a woman. “Treating you like a woman” basically means being dismissive of your experience or knowledge or tone policing (if I make a rude joke under a femme username, people downvote the hell out of it unless it’s about a very safe target- that’s how minor the difference is, to be clear). I’m also probably an egg, so my perception of not being treated like a woman as nice might be skewed.
Some time ago, I had the contrary thought of everyone being a man, so I used to think that just the way you described, everyone was a woman. I don't know what happened to that thought, though. By the way, ::: spoiler I'm a GIRL!
Guy In Real Life
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