I tell you this as an American who's spent enough decades on this earth hearing English, American apartments are rented 99.9% of the time.
I tell you this as an American who's spent enough decades on this earth hearing English, American apartments are rented 99.9% of the time.
It's not "just vernacular", it is perfectly proper formal English. For many non-Americans – and even it seems many Americans too – calling something an "apartment" says nothing about the legal structure of building ownership.
I can find heaps of American news stories about people in the US buying apartments. Random example, this 2007 story from Fox News about the disappearance of a college student in Madison, Wisconsin [0]. It says regarding the victim that "Nolan, originally from Waunakee, had recently bought an apartment and moved to Madison from Whitewater, where she went to school". If Fox News is talking about people buying apartments in Madison, Wisconsin, then it is perfectly normal American English. Much more convincing than random Americans on HN telling me it isn't.
[0] https://www.foxnews.com/story/cops-look-at-bars-surveillance...
For the record - to non Americans (both the majority of the world and the majority of the english speaking world) - "apartment" refers to the type of dwelling, not the ownership status. For many readers this localised hidden meaning in a common term is not obvious.