One of the biggest challenges when developing for iOS is dealing with the ever-changing hardware and software requirements. For example, when Apple released iOS 13, many developers had to update their apps to be compatible with the new version of iOS. This often meant making changes to the code, updating the user interface, and testing the app on the new version of iOS. Additionally, Apple often releases new devices with different screen sizes and resolutions, which can also require developers to make changes to their apps in order to ensure they look and function correctly.