https://appleinsider.com/articles/20/09/09/apple-halts-ios-1361-code-signing-following-ios-137-release
Apple halts iOS 13.6.1 code signing following iOS 13.7 release | AppleInsider
Apple on Tuesday ceased signing code for iOS 13.6.1, effectively barring users who updated to the latest iOS 13.7 operating system from downgrading.
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