Apple has released a series of videos for developers showing how their apps will appear on the upcoming iPhone Duo. Without modifications, apps could look unattractive on the new device's dual screens. Apple encourages using the latest Xcode 27.1 development tools, which include an updated preview module to test apps in four layouts: closed portrait, closed landscape, open horizontal, and open vertical.

Existing apps will display full screen on the front but only partially on the inner screen, with content aligned left and avoiding the camera cutout. Developers who rebuild their apps with Xcode 27.1 can take advantage of the entire inner screen width. Apple notes that older apps that haven't been updated will appear with black bars, similar to the early iPad scaling issues.

Apple's John Ternus criticized previous foldables, saying they were like "two phones awkwardly stuck together," with movies boxed in by oversized black bars. He emphasized that the iPhone Duo's design requires apps to support all new layouts to provide a seamless experience. Developers are urged to update promptly to avoid poor user experiences.