In the sitemap editor, it was previously possible to create “nested” galleries using the context menu. A “nested” gallery is a gallery that was created in a folder that is itself a gallery.
Such “nested” galleries make content storage unnecessarily complex and are also not supported by other dialogs, such as the “Optimize Gallery” dialog.
For this reason, the ability to create nested galleries has been removed from the sitemap editor. This is still possible via the file explorer, but is not recommended.