What’s funny about those “grammar purist” people is singular “they” has been accepted common use in English for centuries, even older than singular “you”. For some reason society got it in our collective heads in the fairly recent past that it was improper grammar, though, and that’s what teachers often teach. I’m still not over my 5th grade teacher marking me down a point on an essay because I used singular “they”. You’re still wrong, Mrs. B.