First some basic information about modern/classic sites:
- The difference between a modern and a classic site is only graphical in the user interface, e.g. site settings shows fewer options even if the missing options are still available if you know the URLs to their settings’ pages.
- In a classic site, all lists and libraries are modern lists/libraries.
- There are several web parts in classic sites that are not available in modern sites.
- There are currently no features that are available in modern sites that are not available in classic sites.
- In a classic site you can create modern pages.
- If you create your own SPFx web parts (SharePoint Framework web parts) they can be used in both modern and classic sites.
- It is also possible to connect a classic site to an new Office 365 group.
- Modern sites do not subscribe to content types from the content type hub.
All workspaces that are created from MetaShare are currently based on classic sites.
Here you find a reference where you can read more about the modern and classic sites: SharePoint classic and modern experiences.