E.g. in cell K1: "=unique_sorted_concat_snb(A1:F10,",")

Code:
Function unique_sorted_concat_snb(c00, c01)
    With CreateObject("System.Collections.ArrayList")
        For Each cl In c00.SpecialCells(2)
          If Not .contains(cl.Value) Then .Add cl.Value
        Next
        .Sort
        
        unique_sorted_concat_snb = Join(.toarray(), c01)
    End With
End Function