Harold Meachum lives in an upper floor of an iconic Art Deco building--so described by Joy--in Manhattan. What real-life building is used in the exterior shots?
According to https://untappedcities.com/2017/03/20/nyc-film-locations-for-iron-first-on-netflix/5/ the apartment is supposedly located at 570 Lexington Avenue, NYC (RCA Victor building). The interior is a build set.
Wiki/pics of building:https://en.wikipedia.org/wiki/General_Electric_Building