As someone who's a mod for a few LGBTQ specific comms on blahaj and is in the blahaj mod chat (keep in mind that I'm not an admin btw) I can confirm that there's been some brigading of specifically this instance and it's users (because it's tied for position with hexbear as biggest trans focused instance on the lemmyverse, it's widely federated so more visible to transphobes, and the users on hexbear are basically psychotic so anyone wanting to harass trans people tends to go for the squishier target of trans people here rather than go to hexbear and get dozens of replies telling them to post pictures of their dick, sending them pictures of a pig shitting itself and calling them a "hitlerite KKKracker" that deserve to be executed by firing squad and then being off and on harassed by the bears for the next two weeks) by transphobes in the past but normally it's just one or two people doing it at once across a load of alts and they pretty quickly get banned. Also since the admins are in Australia, sometimes it takes a while for accounts to be removed and get site wide bans because admins are asleep when trolls from Europe and America are active so the transphobic comments get seen by more people before they get ban hammered.

At one point there was a pair of tiny instances that had open sign ups and literally no moderation that accounts were just being made on with the specific purpose of harassing trans users on here but they got defederated. By now, most of the overtly transphobic people have gotten bored though and stopped doing it.

There's also the occasional problem with the sort of "i'm just asking questions" transphobic gender critical stuff the person you're replying to was mentioning, but because that mainly comes from people using their actual long term accounts and not just trying to drive by harass users here, once they get banned they usually don't tend to come back; since Lemmy's growth has slowed now, a lot of the bad gender critical people have been banned by now and there's not many new ones coming in.

TL;DR: there's been problems with overt and covert transphobia in the past but it's mostly been dealt with by now but we still get the occasional thing every now and again.