Edit; Looked harder, its DrossDrawings on NG's... Was not at all expecting that, not for the feignt of heart for sure ;). Now with Reddit gone, I think I'll have to finally get back on Newground, for other reasons of course
The way I've heard it is this: People tend to use the same sorts of social media as the gender they were assigned at birth. Or, to put it another way, they don't change social networks when they discover themselves and/or transition. Reddit and its descendants Lemmy and Kbin are dominated by AMAB users, and therefore see more transfem users than transmasc users. I'm assured there are a lot more transmasc people on Tumblr.
There's no reason to expect symmetry in gender dysphoria experienced by AMAB and AFAB bodies. There are no strong evolutionary pressures creating that symmetry. I've seen surveys in the U.S. reporting ratios upward of 6:1 transgender women to transgender men.
So first of all I don't know shit about anything, but here's what I'm thinking. There's an extant misogyny/dislike of femininity in society, such that when AMAB people want to be feminine, society looks down on it, but when an AFAB person wants to be masculine, societies like, yeah that makes sense since men are better. So a subset of AFAB people who might have had gender dysphoria, have it alleviated by being able to be tomboys or butch with less societal pressure than AMAB people who want to do femininity would get. Leading to less potential trans men realizing they are trans. But also the "nature" part of the nature/nurture composite could account for it as you've said.
Are there any evolutionary pressures pushing anything? Symmetry is essentially the default, I'd assume. Isn't the ratio of gay to lesbian roughly the same?