main.dart

void main() async {
  await variant1();
  variant2();
  print("xxx");
}

Future<void> variant1() async {
  final result = await y();
  // async gap
  print("y: $result");
  
  final result2 = await x();
  // async gap
  print("x: $result");

  print("aaa");
}

void variant2() {
  y().then(/* async gap */ (result) {
    print("y: $result");

    x().then(/* async gap */ (result2) {
      print("x: $result");
      
      print("aaa");
    });
  });
}

Future<int> y() async {
  return 1 + 2;
}

Future<int> x() async {
  return 2 + 3;
}