question

Not directly, as far as I know. There sadly is no direct method to get the week in the Datetime class. You can still use the remaining methods to calculate the week though.

string date = "01.01.2021 08:22";
// Construct datetime from string
DateTime dateTime = DateTime(date, "%d.%m.%Y %H:%M");
int weeks = 0;
int curYear = dateTime.year;
// Find previous monday
while(dateTime.dayOfWeek != 2)
{
    dateTime -= DateTime(86400);
}
// Check if year changed
if(dateTime.year != curYear)
{
    if(dateTime.day > 28)
    {
        // Is first calendar week
        return 1;
    }
    // Is part of last year's last week
    curYear = dateTime.year;
}
// Go to start of year
while(dateTime.year == curYear)
{
    dateTime -= DateTime(604800);
    weeks++;
}
// Check if week belongs to current or last year
if(dateTime.day > 28)
{
    weeks++;
}
return weeks;