Or

Sub GetCommonValues()
Dim oSD As Object, rMyRng As Range, nEndRw1 As Long, nEndRw2 As Long, r As Range

Set oSD = CreateObject("Scripting.Dictionary")
    nEndRw1 = Cells(Rows.Count, "A").End(xlUp).Row
    nEndRw2 = Cells(Rows.Count, "B").End(xlUp).Row
Set rMyRng = Union(Range("A2:A" & nEndRw1), Range("B2:B" & nEndRw2))

Application.ScreenUpdating = False

With oSD
    .CompareMode = False
    
    For Each r In rMyRng
        If Not .Exists(r.Value) Then .Add r.Value, 1
    Next r
    
    Range("C2").Resize(.Count, 1).Value = Application.Transpose(.Keys)
End With

Application.ScreenUpdating = True

End Sub