main.dart

void main() {
  final dt = DateTime.now().toLocal();
  
  final deviceTimezoneOffset = dt.timeZoneOffset;
  final offsetHours = deviceTimezoneOffset.inHours.abs().toString().padLeft(2, '0');
  final offsetMinutes = deviceTimezoneOffset.inMinutes.remainder(60).abs().toString().padLeft(2, '0');

  final offsetSign = (deviceTimezoneOffset.isNegative) ? '-' : '+';
  final offsetString = '$offsetSign$offsetHours:$offsetMinutes';
  
  print(dt.toIso8601String().substring(0, 19) + offsetString);
}