the code itself:

Sub test()
Dim myrng As Range, cl

Application.ScreenUpdating = 0

With ActiveSheet
    
    .Range("a1").CurrentRegion.Borders.LineStyle = xlContinuous
    
    Set myrng = .Range("b2", .Cells(Rows.Count, "b").End(xlUp).Offset(1))
    
        For Each cl In myrng
        
            With cl
            
                If .Value <> cl.Offset(1).Value Then
                
                    With .Resize(, 11).Borders(xlEdgeBottom)
                        .LineStyle = xlContinuous
                        .Weight = xlThick
                    End With
                    
                End If
            
            End With
            
        Next
    
End With

Application.ScreenUpdating = 1

End Sub