> I’m sure there are examples, but in common use it is understood to be plural and has been used that way in all writing for a long time.

It is grammatically plural, but it has been accepted for semantically singular use since long before the Victorian effort to impose Latin-inspired rules on English usage which failed to eradicate it despite intense effort. (Victorian prescriptivism did have some good effects — regularized spelling FTW — but trying to eradicate clear and useful usages like singular “they” was one of its less-well-considered, but fortunately also less-successful, efforts.)