flutter app exit suddenly when launch directly from device

In iOS 14+,debug mode Flutter apps can only be launched from Flutter tooling, IDEs with Flutter plugins or from Xcode. Alternatively,build in profile or release modes to enable launching from the home screen.

Please run in release mode by the following way:

flutter run --release

By the way, if you got the null check error as: Error (Xcode): Error: Cannot run with sound null safety, pease add ` — no-sound-null-safety` option:

flutter run --release --no-sound-null-safety