> No, and it’s frustrating for people who had it hammered into their reading and writing habits all through school. I can’t read a singular “they” without mentally tripping on it.

If you mean "no" in the sense that this specific sentence isn't true:

> Hasn’t it always been the case that you could use “they” as a way to refer to a singular human without implying any gender?

then you are mistaken, as sibling comments point out. Certainly there is a history of teaching people not to use singular 'they' (I don't know how long, but I was certainly taught it), but people have actually been using singular 'they' for a long, long time, and usage trumps fiat at least in English.

Singular-they constructions have been in English for literally hundreds of years.

Tell it to my English teachers from grades 3-12

Sure, point me to them.

I learned a lot of wrong things in school. One could say I have spent most of my adult life unlearning them. Welcome to the club.

Consider also James Loewen's classic book, too: https://www.amazon.com/Lies-My-Teacher-Told-Everything-dp-16...