The Site Collections module is used as a SharePoint data store. A site collection is a grouping of websites under a common top-level site that have the same owner and share administration settings, for example, permissions. When you create a site collection, a top-level site is automatically created in the site collection. You can then create one or more subsites below the top-level site.
In the modern SharePoint experience, every site is a site collection and can all be associated with a hub site, making the architecture more flexible and adaptive to changes.
Site Collections Module Settings
Module Settings for Modern
Under the ‘Modern Sitecollections’ tab, administrators can get an overview of current site collections, as well as remove the ones you want to get rid of.
The list of of modern site collections has a remove button which unregister the modern site collection from the Enterprise database so you can apply another site type but it does not uninstall Enterprise (Wizdom) components from the site collection and does not delete the site collection.