I believe the term Tumbler uses for what I am is "Net gender." It means that IRL, I do have one of the binary genders. (I refuse to say which right now.) However, so long as I'm online, I refuse to reveal what my gender is to such an extent that I have actually become, to an extent, non-binary so long (and only when) I am communicating via a screen over the internet.
It shows my age to some extent, it is most prevalent in 90s kids, those who grew up in early days of the internet when parents had the (very legitimate) concern over their children revealing personally identifying information online and schooled us not to. These days, Face Book has unfortunately altered that approach. However, I caught on to cancel culture's activities early and clamped back down on the bad habits I was starting to pick up from social media. Since then though, I actually have started to legitimately see myself in non-gendered terms while online, and I get a strange thrill when someone guesses my gender and guesses wrong.