Panel 1: A person with the text "Singular 'they'" written on them smiling with open arms.
Panel 2: "Singular 'They'" beaten up by others who said, "Singular they is ungrammatical. It's too confusing," "How can anyone use plural pronouns for singular," and "Every pronoun should only have one purpose."
Panel 3: "You" hiding from the mob who was beating "Singular 'They'"
Panel 4: "German 'Sie'" hiding with even more fear next to "You"
See my other comments in this thread as well, but using singular they to refer to a specific, known individual was never something that Shakespeare did, and that is the usage that people are up in arms about. Your example uses singular they to refer to an unknown person, which is a usage that's been around for centuries, yes.
It's using they to refer to a single person. Some people think it's only supposed to be used for a group, but that's completely wrong. It's been used to refer to singular people since at least Shakespeare, if not longer. For example: "if some_one_ tells you they is singular, they are mindlessly consuming right wing media and not considering if it's actually correct."
This misses an important distinction that singular they was never used to refer to a known, specific individual until recently, and was certainly never used by Shakespeare that way.
It's just a generic he or she, I've seen it used for years and never thought it's related to any gender identity issues. Also they is easier to type than he/she. It's similar to how vous can be used for plural or singular. Although maybe it's not a thing in places that don't also speak French.