Corresponding to the bio, of course.
In my beloved Atlantic City, NJ USA, transfolk are fairly commonplace. Pretty obvious transwomen have been in public restrooms with me, and it's not any kind of issue. For that matter, women occasionally jump in the men's room if the line is too long at the women's restroom.
If you can line people up in the shower, and you have all innies, and one outie, it's reasonable for the comfort of all to...uh...standardize that a bit. I mean, if a transperson feels like they are in the wring body (which I have the greatest sympathy for), being in the 'wrong' locker room seems pretty trivial.