Macro si

Sub Macro20()
If Feuil2.Range("$AL$19").Value = 20 Then
    Range("AL27:AR28").Copy
    Range("N18:T19").Select
    Range("N19").Activate
    ActiveSheet.Paste
    Range("K27").Select
End If
End Sub

Private Sub Worksheet_Change(ByVal Target As Range)
    
    If Not Application.Intersect(Target, [AL19]) Is Nothing Then
        If Target.Value = 20 Then Macro20
    End If

End Sub

Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
    If Target.Address = "$AL$19" And Target.Count = 1 Then
        If Target.Value = 20 Then
            Application.EnableEvents = False
            Macro20
            Application.EnableEvents = True
        End If
    End If
End Sub