I think you’ve fallen into a trap that a lot of writers fall into… any one of my characters could be transgender because I’m writing about human beings. Plays have become about ‘issues’ - which means characters become a political or social mouthpiece for the author and the authors world. What you’re talking about is whether a cis-person could write a convincing trans mouthpiece character - the answer, as you’ve suggested, is yes with enough research - but it’s reductive. Trans people are just people, so if you write a character who stays at home and enjoys Christmas and struggles with buying their partner a gift but picks the right gift in the end - and that’s the full extent of your story, then why would that character not be trans? The idea that trans characters must only ever talk about being trans is a terrible trap for trans writers to fall into - it’s both insulting and limiting and turns trans writers into a single flat monolith. Good writes write good stories, that’s it. Everything else is agitprop.