Userform Listbox Conditional on Previous Selection

Try replacing your code with this & see if it is what you want

Private Sub cmdOK_Click()
    Dim ws As Worksheet
    Set ws = Worksheets("Output")
    ws.Cells(1, 1).Value = Me.listMNGR.Value
    Unload Me
End Sub

Private Sub listMNGR_Click()
    Dim lCol As Long
    lCol = Me.listMNGR.ListIndex + 4
    With ThisWorkbook.Sheets("combolists")
        output1.listMC.List = .Range(.Cells(2, lCol), .Cells(2, lCol).End(xlDown)).Value
    End With
    Me.Hide
    output1.Show
End Sub


Private Sub UserForm_Initialize()

    Dim cell As Range
    With ThisWorkbook.Sheets("combolists")
        listMNGR.List = .Range(.Cells(2, 1), .Cells(2, 1).End(xlDown)).Value
    End With
End Sub