As a non-english native, I didn‘t know that. I thought „they“ always meant more than one. What‘s the reasoning if you know the gender? How to differenciate between a group and a person whose gender is unknown?
"Every one must judge according to their own feelings." That's a nice example on how it can be used. Most of the older examples include "every" or "any" before using they. I think I need to study that part of the language as (at least in some situations) it seems like a nice way to get around using a generic form.
In my language journalists created a new word for it that was met with resistance first, but it doesn’t corrupt another word and it has been added to all dictionaries and is used heavily.