Welcome to the forum @threehappypenguins
Perhaps someone with expertise in this area will show up, but meanwhile I’ll point to some resources.
Changing backend type leaves invalid backend options #3082
Microsoft SharePoint v2 (Microsoft Graph API)
--site-id (String)ID of the SharePoint site to store data in. This parameter is required when using the relative document library path (without specifying the SharePoint site’s web address). This ID can be looked up by querying in the Microsoft Graph Explorer. When the SharePoint site’s full web address is provided, it is looked up automatically.
No backup without “–no-backend-verification=true”
This was helpfull to find the “site-ID”