By default, the FieldChooser context menu is displayed when you right-click on the ColumnHeadercell of the Grid but it is not displayed when you right-click on the Grid cells.
When you try to use your own context menu along with the FieldChooser context menu item, it overrides the FieldChooser context menu.
The context menu that is displaying when you right-click the ColumnHeadercell can be restricted by the TableControlMouseDown event. By using this event, you can customize ContextMenuStrip to display only in the cells other than the header cells.
The following screenshot displays the context menu.
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