Probably. For Lemmy instances, read the community rules in the sidebar and instance rules on the instance (in the sidebar when viewing the top-level page).

You could also start your own community on some instance that doesn’t take issue with it, or even start your own instance if you’re willing to set up and run one.

EDIT: Now you kind of made me curious, and I thought that I’d skim some instances running 0.19.11 (an up-to-date version, so are presumably reasonably maintained). Part of the problem is that there are probably a number of things that instances might (and often do) prohibit, and what an admin might consider objectionable probably ranges from party to party. Like, say you said that you wanted to have a good-faith discussion on the impact of transexuality, weren’t going to criticize any individuals involved, and were going to be polite. That might pass muster with some places that have comparatively-restrictive rules…but hard to know in advance.

• Some straight-up have an explicit prohibition on transphobia.

• Some prohibit harassment.

• Some prohibit being “unkind” or similar.

• Some ask a user to be “respectful”. What that entails probably differs from person to person in interpretation.

Might ask an admin in advance.

Going through a couple of general-use instances, some that I would guess, from the rules text, probably are going to be on the more-permissive side:

• lemmy.libertarianfellowship.org says that they specifically take issue with censorship on many instances. They say that they do have some rules, but nothing on their rules page seems to prohibit criticism of transexuality.

• discuss.online has a “be nice”-type set of guidelines.

• real.lemmy.fan has no explicit prohibition other than on harassment and asks users to be kind.

That being said, if you think that you’re gonna say something that might raise hackles, maybe ask the admin(s) there to clarify whether it’s something that they’d take issue with.