“They” and “them” can be used as singular gender-neutral pronouns in English. A common everyday example is:
Person 1: I went to see my dentist today.
Person 2: What did they say?
I’ve heard variants of the above since the nineties, but this is not at all a modern trend. The following is example from William Shakespeare (1594):
There’s not a man I meet but doth salute me
As if I were their well-acquainted friend.
Note the usage of “their”, referring to the singular noun “a man”.
The following example is from Jane Austen (1813):
To be sure you knew no actual good of me —
but nobody thinks of that when they fall in love.
The key is that “nobody” is grammatically singular: we say “nobody is here”, not “nobody are here”.
The following Biblical example (James 2:15–16) uses “them” in singular:
Suppose a brother or a sister is without clothes and daily food.
If one of you says to them, “Go in peace; keep warm and well fed,” but does nothing about their physical needs, what good is it?
Examples of this usage go back at least as far back as the 14th century.