I can't imagine going without writing one. One of the reasons I'm still alive right now is that I've procrastinated on writing my letter.
It would be addressed to my sister, the one person I care about and who cares about me, and it would just be describing the pain I've been living with and trying to help her understand that it wasn't a selfish act; it was an inevitable ending to a sad short story. I want her to know that I care about her and that the only reason I haven't attempted suicide every single time I saw a bottle of pills or walked by a road was that I didn't want to hurt her and it finally became too much to carry.
I'd probably write a smaller one to the police as evidence just to say "this is no one's fault, don't waste your resources searching for harassment, etc." and mail the longer letter to my sister right before doing it. I've heard too many stories about police confiscating suicide notes before the intended recipient is able to read it (at least for a while) to leave it in their hands.
I might also make a brief post on social media vaguely coming out as trans in a way that would try to help people understand where we're coming from. Something short and vague that doesn't explicitly scream "I'm trans and I'm going to CBT, call the police" but is easily interpretable later on if you know that I CBTed right after posting it. "why can't people just let trans people be" and then "thanks texas" or "dealing with dysphoria's hard enough without all of the discrimination and hatred" but I'm still not sure if that would make it better or worse for trans people still living.