Singular "they" dates at least back as far as the 14th century, and I've yet to meet a person who objects to it but does not use it themselves now and again without even noticing if you observe them speak enough. It's entirely integral to English.

The interlude during which some pushed for "they" to be exclusively plural, was a mere brief blip in the history of the language.

It's also a couple of centuries older than singular "you", so if you want to complain about a pronoun changing between singular and plural, that's a better candidate.

In commonwealth english "they" can and frequently does work to indicate a singular person.

Here it's clear the word is referring to a singular stranger.

What word would you use instead in this specific case?