More than a solution it's a workaround
1)I changed the btn.click to cbx.selectedindexchanged but it will be instantly pasted into the textbox but have the same result except for the click (I'll wait for some other solution)
2)Make for some
Public Sub btn_Click(sender As System.Object, ByVal e As System.EventArgs)
'Dim btn As New Button
'btn = CType(sender, Button)
'Dim txt As New TextBox
'txt = CType(sender, TextBox)
Dim cbx As New ComboBox
cbx = CType(sender, ComboBox)
TextBox4.Text += cbx.SelectedItem.ToString & vbCrLf