I was just thinking about that this morning, for unrelated random reasons. Or maybe it's serendipity. Anyway, English has sort of repurposed "you" to work as what you're calling a fourth-person pronoun. Often we mean "you" as second person. Maybe usually we do. But when we say something like, "You can't smoke here," we pretty much aren't speaking of a specific person. Our general sentence is understood.

But French, one of the other languages I speak fluently, is moving in a different direction!

The pronoun "on" has been used for centuries as a general, fourth-person pronoun. (Technically grammatically, it's a third-person singular that doesn't refer to a specific person, but always to people and never to inanimate objects or animals.)

"On ne fume pas ici," might be best translated into modern English as, "You can't smoke here," in the generalized fourth-person sense.

But!

In spoken French in the last century or so, "on" has come to almost entirely replace "nous" as the actually used first-person plural, "we."

This is despite the fact that "on" is technically neither first person nor plural!

Just goes to show what slippery critters pronouns truly are. 🤣