In North American lingo, "apartment" exclusively means a multi-family unit that you rent and don't own. If you own a multi-family unit it is a Condo (condominium) and never refered to as an Apartment. I know, confusing.

Also, duplexes are houses with two units in them vs. a two floor apartment.

That’s entirely dependent on the region. In Chicago, two-floor apartments are routinely referred to as duplex. In Cleveland, a duplex is a house with two dwellings, too and bottom. If the house is split side-by-side, it’s a double. There are other places where these two terms are reversed.

That’s a stacked townhome.

On the 30th floor of an apartment building?

Hmm I interpreted “two floor apartment” incorrectly it seems.

I don’t think there are many of them in the states except for maybe a few penthouses.

I live in North America. While this is technically correct, people can and do use the terms loosely as well.

And regardless, you can most definitely rent a house.