Problem showing a listbox with selected items using .ShowModal

The form is not yet shown when you are setting the selected property of the item and therefore cannot be set.

You need to add an event handler for the OnShow event of the userform and set the selected property after the form is shown.

With UserForms.MyForm.ListBoxABC
  .Add("Test_01")
  .Add("Test_02")
  .Add("Test_03")
End With
'

UserForms.MyForm.ShowModal 

Sub OnShow_Handler(Sender)
    'Set this handler under the events section for the form in the designer
    UserForms.MyForm.ListBoxABC.Selected( 0) = True
End Sub

Reference event handling here.