From Xojo Documentation
Forces an update of the menu bar and executes the EnableMenuItems event handler.
In most cases, the standard menu bar updating will be sufficient. There are cases, however, when it's not. For example, if the SelChange event handler of a TextField control causes all of the menu items in a particular menu to be disabled, the menu itself should be disabled. Unfortunately, it won't be because the user has not yet clicked in the menu bar. Under circumstances like this, you can call the EnableMenuItems method to force your app to only update the menus based on your own conditions.