Looking for a way to calculate the last Monday of any Month

     There may be an easier formula but this is the one I came up with.   Requires 2 Calculation fields and a Date field. 

     days and LastMondayMonth.

     days calculation

     DayOfWeek(Date (Month (CurrentMonth) + 1; 0; Year (CurrentMonth)))-2

     LastMondayMonth Calculation

     Case(days ≥ 2;Date (Month (CurrentMonth) + 1; 0; Year (CurrentMonth))-
     (DayOfWeek(Date (Month (CurrentMonth) + 1; 0; Year (CurrentMonth)))-2);
             days<0;Date (Month (CurrentMonth) + 1; 0; Year (CurrentMonth))-6;
             days=0;Date (Month (CurrentMonth) + 1; 0; Year (CurrentMonth));
             days=1;Date (Month (CurrentMonth) + 1; 0; Year (CurrentMonth))-1
     )

     Let ( [ Dt = YourDateFieldHere ;
               DtLast = Date ( Month ( Dt ) + 1 ; 0 ; Year ( Dt ) ) ]; // this is the date for the last day of the same month
               DtLast - Choose ( DayOfWeek ( DtLast ) ; 0 ; 6 ; 0 ; 1 ; 2 ; 3 ; 4 ; 5 )
           )