This option lists all the post types having
show_ui set to
true: i.e., the post types which have a default user interface to add and manage items.
By default, only the standard
page types are enabled. Selecting a checkbox enables the plugin for the corresponding post type.
If a post type is enabled, but a plugin or some other code hides the default UI in favour of a custom one, there is a chance that the links added by Duplicate Post won’t be visible. If so, feel free to contact me so we could try to find a solution.