This is absolutely a trans-inclusive community, it just isn't spelled out (e: it is now) because inclusion should be natural. I don't like making assumptions about a person's identity or beliefs (unless they scream it to the heavens, at which point it isn't an assumption anymore), and I can't determine whether a person is welcome here based on what they are. When a person's behaviour becomes problematic, that is when I step in. In particular, if someone reports a homophobic, transphobic, or racist comment, you won't see me argue with them: those comments get immediately deleted and the user permanently banned. Fortunately, nearly all community members I've seen are friendly, or at least polite, with LGBTQ+ folk.

Regarding the meme in question. There is an argument to be made that just using the media as a meme, even of an unrelated topic, gives the author unwanted exposure. I don't think this applies in this community, or most of the fediverse (excepting places like Grad or Hexbear). We all know that JK is morally inferior to what came out of my dog this morning. Seeing this meme won't change that position, nor does it try to glorify her morals or justify her views. It is the essential meme: a well-known scene from popular culture, removed from its environment, to express an idea or sentiment that is common within this demographic.

If it were against the rules, I'd have reported it.

Instead, I made a snarky comment, because even though it's not against the rules, the less Rowling in the world, the better.

There's a lot of trans people in linux and foss communities

in a community full of trans folk

which by the phrasing is what Ada is saying, not that it's specifically a trans community