VBA Userform Issue - Command Button / msg Box

The problem is you are testing for False on selected items. But the selected property is a array of True/False elements, one for each item. So even if one is selected all the others will be false.

This examples uses a function to determine whether an item has been selected or not.

Function ItemIsSelected(Lst As msforms.ListBox) As Boolean
    Dim lngIndex As Long
    For lngIndex = 0 To Lst.ListCount - 1
        If Lst.Selected(lngIndex) Then
            ItemIsSelected = True
            Exit Function
        End If
    Next
End Function

Private Sub CommandButton1_Click()

    If ItemIsSelected(ListBox1) Then
        MsgBox "Output Items"
    Else
        MsgBox "No items selected"
    End If
    
End Sub

Private Sub UserForm_Initialize()

    ListBox1.List = Application.WorksheetFunction.Transpose(Range("A1:E1"))
    ListBox1.MultiSelect = fmMultiSelectExtended
    
End Sub