Here's an example: If someone wants to really enjoy fine food, then you should direct them to this restaurant.
Or how about this: I don't know who it was that sent me that nasty message but they really ought to know better.
Or this: If you have a family member who needs help, make sure they see us.
Are any of the OK? We say no, no and no.
No, because you do not use a plural pronoun to refer to a singular -- in each of these cases, a single person.
But lately, some self-appointed apostles of political correctness have latched onto they as entirely appropriate, especially since they argue that we're supposed to be gender neutral and embrace a non-binary gender world. After all, they say, people can now choose whether they want to identify as he, she or neither.
Well, from a strictly grammatical viewpoint we're just not buying it. No way!
Let's look at that first sentence again: If someone wants to really enjoy fine food, then you should send him or her to this restaurant. Correct!
And let's look at that third sentence again: If you have a family member who needs help, make sure he or she sees us. Correct again!
And of course the same adjustment should be made for the second sentence.
This is standard, accepted, correct grammar.
But please, don't take our word for it.
Go to The New Yorker, a magazine that has been a model of correct grammar for nearly 100 years and also a very liberal (some might even say progressive and politically correct) publication these days.
Here's a excerpt from The New Yorker's lead article in its December 30, 2019 issue:
. . . that someone reads The New Yorker only for the cartoons. Or that he or she always reads the cartoons first.There it is.
Straight from The New Yorker.
We rest our case!