OneNote Class Notebooks created with SharePoint app v created with App Launcher in OneDrive

I feel there are a few things to mention here.

The first is yes you can move notebooks between OneDrives and OneDrive or onedrive to sharepoint (Groups, Teams, SPO) using the API.

The app that was added to sharepoint is no longer supported and theres no further development to this.  You are going to get the features you from either the Class Notebook, Teams or the API.   I don't think Microsoft will get rid of the app launcher version of the Class Notebook and force us to use Teams.  It would be a real shame if they did as so many use this and not ready for Teams.  Teams isn't for everyone (from what we are seeing with our customers) but they do still want the notebook.

You can still create notebooks in SharePoint using the API.  We have done some extensive work around this and have built a solution that will create all the notebooks in a SharePoint Online Site Collection based on the OneNote API and your MIS. Works great once you understand how the API, timeouts, throating etc work