I was facing the same issue and promoting this error message while submitting the app on the AppStore - ITMS-90725: SDK Version Issue - This app was built with the iOS 13.7 SDK. All iOS apps submitted to the App Store must be built with the iOS 13 SDK or later, included in Xcode 11 or later. Further, starting April 26, 2021 iOS apps submitted to the App Store must be built with the iOS 14 SDK or later, included in Xcode 12 or later. But I saw my build is in processing on the TestFlight even showing the above error so concluded that it is just a bug of the Xcode