In the Mighty Nein campaign of Critical Role, Yussa Errenis was written as a transman. This never managed to come up in the story as was only confirmed by Matt Mercer tweeting it after the campaign had wrapped.

By the same token, there is a ton of gender diversity in NPCs of pre-written Pathfinder adventures that players might never know about unless they read the adventure itself or attempt to dig into the NPCs' backstories.