How to create a ComboBox content control in word(2019) by OpenXML sdk(C#)?

I use code(see below) to create ComboBox content control in word. This ComboBox control work. But there is issue in this control. Word user can focus into options and change the text of that option.

Following is the code:

    static SdtBlock CreateComboBoxSdtBlock(string title, string[] items, string selectedValue)
    {
        var comboBox = new SdtContentComboBox();
        foreach (var item in items)
        {
            comboBox.Append(new ListItem { DisplayText = item, Value = item });
        }

        return new SdtBlock(
            new SdtProperties(
                new SdtAlias { Val = title },
                new Tag { Val = title },
                new Lock { Val = LockingValues.SdtLocked } 
            ),
            new SdtContentBlock(
                new SdtContentRun(
                    new Paragraph(new Run(new Text(selectedValue))), 
                    comboBox
                )
            )
        );
    }