flutter - How to build APK with no sound null safety

Question

I can run an app in release mode on my phone with passing flag --no-sound-null-safety --release, but neither flutter build apk --enable-experiment=non-nullable nor flutter build apk --no-sound-null-safety nor flutter build apk --enable-experiment=non-nullable --no-sound-null-safety will work

Answer 1

It was only necessary to use additional comment // @dart=2.9 before all imports in main.dart so it could run without any flags