Amend code

Sub Sample()
    Dim TotColumns()
    Dim I As Long, LastRow As Long
    
    FinalCol = Sheets("Details").Range("A1").End(xlToRight).Column
    
    Application.ScreenUpdating = False
    
    ReDim Preserve TotColumns(1 To FinalCol - 2)
    For I = 3 To FinalCol
        TotColumns(I - 2) = I
    Next I
    
    With Sheets("Details")
        .Range("A1").Subtotal GroupBy:=6, Function:=xlSum, TotalList:=TotColumns, _
        Replace:=True, PageBreaks:=True, SummaryBelowData:=True
    
        LastRow = .Range("A" & Rows.Count).End(xlUp).Row
    
        For I = LastRow To 2 Step -1
            If InStr(1, .Range("B" & I).Value, "Total", vbTextCompare) Then
                .Range("F" & I).Font.Bold = True
                .Range("F" & I).Value = Range("F" & I - 1).Value
                .Range("C" & I).Copy Range("B" & I)
                
                .Rows(I + 1).Select
                Selection.Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
            End If
        Next I
    End With
    Application.ScreenUpdating = True
End Sub

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