properly convert string to datetime code example
Example 1: convert string date to datetime and format
var dateString = "2020-09-25T10:13:21.246321+01:00";
String formattedDateString = DateFormat('do LLLL yyyy').format(DateTime.parse(dateString));
// formattedDateString - OUTPUT: "25 September 2020"
Example 2: c# string to datetime
.Net str to DateTime