From what I understand transplaining is people telling trans people all about trans. Having an opinion about it, in other words.
You're not allowed to explain to a Trans person anything about trans.
Because, talking about the dangers of transing children, prison statistics, or AGP is forbidden. So they pretend that it's 'transplaining'. Keep your nose out!
Ignoring the massive elephant in the room which is how they can 'womansplain' what woman means. That, obviously, is completely fine.
They can tell you exactly what it means to be a woman because it's a feeling deep inside. And you must listen, and change your viewpoint of it means to be a woman. Despite, you know, actually being one.
But talking about statistics, evidence connected to transgenderism? Nooo.