Since you referenced a Window, I’m assuming MacOS application, not iOS. Probably the same, but not sure since I don’t program for iOS.

According to the documentation, applicationDidFinishLaunching is called by NSApplication just before entering into the application event loop. You could try applicationWillFinishLaunching, which is called just after the application object is initialized, which should be before any controllers are created, if that is appropriate. You could also override the init() method (Swift or Objective-C) if that makes sense.

Jonathan