Hello to all,
I found online this macro highlighting duplicate values:

Sub colora_duplicate()
 
    Dim t As Single
     
    t = Timer
    Dim q&, X&, i&, a
    Dim ash As Worksheet
    Set ash = ActiveSheet
    q = Range("A" & Rows.Count).End(3).row - 3
    a = Range("A2").Resize(q)
     
    Application.ScreenUpdating = False
     
    ActiveSheet.Unprotect "123456"
     
    With Sheets.Add
        .Cells(1).Resize(q) = a
        .Cells(2) = 1: .Cells(2).Resize(q).DataSeries
        .Cells(1).Resize(q, 2).Sort .Cells(1), 1, Header:=xlNo
             a = .Cells(1).Resize(q + 1)
                           
        For i = 1 To q
            If a(i, 1) <> a(i + 1, 1) Then
                If i > X + 1 Then _
                    .Cells(X + 2, 1).Resize(i - X - 1).Font.ColorIndex = 3
                X = i
            End If
        Next i
         
        .Cells(1).Resize(q, 2).Sort .Cells(2), 1, Header:=xlNo
        .Cells(1).Resize(q).Copy ash.Range("A2")
         
    Application.DisplayAlerts = False
        .Delete
    Application.DisplayAlerts = True
     
    End With
     
    ActiveSheet.Unprotect "123456"
     
    Call centra_colonna
    Call rimetti_formula
     
    Application.ScreenUpdating = True
     
    'MsgBox "Code took " & Format(Timer - t, "0.00 secs")
    MsgBox "controllato in " & Format(Timer - t, "0.00 secs"), 0, "Avviso"
 
    End Sub

you can a change?
Now if this is a duplicate value is highlighted.
The change is to add the word "duplicate" in cell C
If not duplicate add the word "not duplicate."
I hope I was cpmprensibile.
A greeting,
max_max