Customizable pronouns

[Gwenorai]

https://en.wikipedia.org/wiki/Singular_they

Dates to the 14th century, if Wikipedia is correct.

It is still heavily argued to be plural. Even if it was used back in the 14th century, it can just be argued that those works were grammatically incorrect. Shakespeare does that a lot. Just because it's old doesn't mean that it's correct. Hopefully, in the future it will be adjusted so that it is widely accepted as singular, right now, it is not. You'll still get marked down for using 'they/them' as singular in papers for example.

What you posted shows a lot of arguments on how people avoid using they/them as singular, preferring to write around it than use it.