For me, its really quite simple as I already have two kind of separate identities. My Facebook and Instagram are my real world identities, so there is very little about being trans or LGBT there (though I am in a couple groups but no one pays attention to what groups you're in LOL). And then my other social media accounts are my online identity. These are the ones where I openly post that I am transgender/non-binary. As I've only come out to a finite amount of people in the real world, my facebook and instagram don't really have much there, although now FB has gender and pronoun options, so I did change my gender to other and pronouns to 'they/their' but no one really has noticed outside of the few people on my list from the LGBT groups I'm in.
Noooooow.... there is a bit of a disclaimer. My online identity accounts all relate to my username, so if you know my online identity, my open identity accounts are easy to find (and I do link some of them on my FB profile) SOOOOO some real world people may end up finding out without my knowledge, but those are only the people who care enough to view my other profiles. And I know for a fact there aren't many of those. None of my family for example looks at my deviantart (thank heavens for that or they'd be flabbergasted... *gasp* She writes GAY STORIES! OH NO! [Use she pronouns, because that's what my family would use])