Add a task C# sample outlook

Outlook.TaskItem task = null;
Outlook.RecurrencePattern recPattern = null;
 
try
{
    task = (Outlook.TaskItem)OutlookApp.CreateItem(Outlook.OlItemType.olTaskItem);
    task.Subject = "Do billing";
    task.StartDate = new DateTime(2013, 06, 25);
    task.DueDate = new DateTime(2013, 06, 25);
    task.Status = Outlook.OlTaskStatus.olTaskNotStarted;
 
    recPattern = task.GetRecurrencePattern();
    recPattern.RecurrenceType = Outlook.OlRecurrenceType.olRecursMonthly;
    recPattern.PatternStartDate = new DateTime(2013, 07, 25);
    recPattern.NoEndDate = true;
    task.Save();
}
finally
{
    if (recPattern != null)
        Marshal.ReleaseComObject(recPattern);
    if (task != null)
        Marshal.ReleaseComObject(task);
}

https://www.add-in-express.com/creating-addins-blog/2013/06/12/outlook-tasks-create-get-delete/