Yes! English speakers have been using they/them as third person, singular, non-specific pronouns for as long as English has been recognizably English. (Recognizable to us modern speakers, I mean.)

You can find Shakespeare and Chaucer both using they/them in the singular, non-specific sense.

It's so built into the language that we often don't even realize we're doing it when we do it. And we do it a LOT.

The recent change, and the one that people seem to object to emotionally, is using it in a specific sense, to describe a particular person.

But their emotional reaction doesn't usually center on the shift in usage from the non-specific to the specific, which is a quite minor but real change.

Instead, they claim that using they/them in the singular is simply wrong. But they're the ones who are wrong, lol, as you so well point out.