Code:
Sub M_snb()
    c00 = Join([transpose(text(date(year(A1),month(A1),0)+row(1:31),"yyyy-mm-dd"))], ",")
    sq = Filter([transpose(if(A1:A200="","~",if(countif(A1:A200,A1:A200)>1,text(A1:A200,"yyyy-mm-dd"),"~")))], "~", False)
    
    Do Until UBound(sq) = -1
       c00 = Replace(c00, sq(0), Join(Filter(sq, sq(0)), ","))
       sq = Filter(sq, sq(0), False)
    Loop

    sq = Split(Replace(c00, "_", ","), ",")
    Cells(1, 6).Resize(UBound(sq) + 1) = Application.Transpose(sq)
End Sub