Starfield is a new IP as much as Elden Ring is a new IP. It's literally Fallout in space; same way Elden Ring is Dark Souls 4.It's a new IP. It's not Fallout or Tes that sells also because of the name
Whether a game is technically a new IP or not is not that relevant when the developer is well-known. All Fallout and TES fans knew about Starfield.