Pro tip: everyone is they/them until otherwise stated. It sounds counterintuitive until you look at the example of the unknown stranger. You see a jacket left on the back of the a chair, and wonder if the stranger will return. You ask a person nearby, “Do you know who this belongs to? When are they coming back?”
English has always used neutral pronouns for someone unknown to you. We constantly make assumptions about gender based on appearance, and cis people take for granted that our outward appearance matches their gender. My best take on being an ally and inclusive is to default to gender neutral pronouns until someone states it or corrects you.