When trying to connect to Sharepoint Online with legacy authentication disabled, the error message below is thrown:
"[System.NotSupportedException] Cannot contact web site 'https://XXXXXX.sharepoint.com' or the web site does not support SharePoint Online credentials. The response status code is 'Unauthorized'"
This is a product defect (33432).
This will be fixed in a future release of the product. If you require this immediately corrected, please contact Support for a hotfix referencing the defect ID 33432.