My issue with this error was with my messages extension. I needed to create another asset catalog in the main app with an iOS app icon and target the main app like mentioned here: https://help.apple.com/xcode/mac/current/#/dev4b0ebb1bb. Then making sure my Messages Icon set was only targeting the extension. Then was getting the error of: The app icon set named “AppIcon” did not have any applicable content but my 1024x1024 app icon was there... Adding the rest of the iOS icons in the set fixed that error. Super frustrating with generic error messages and seeing so many developers with this error for years.