Modern iOS apps heavily rely on dynamic frameworks and XCFrameworks. During the “unpack-ios” phase, Xcode extracts and verifies these embedded binaries. If a third-party framework was built for an incorrect architecture (e.g., only x86_64 for the simulator but included in a release build for a real device), or if its binary is stripped of necessary symbols, the unpacker throws an exception. This is particularly common with vendored binaries that were not properly built for release distribution.
flutter build ios --release