Please note that Cloud storage API's are pretty dynamic. Microsoft in particular loves changing things around. A quick look into the changelog will show how many changes/enhancements and fixes have gone in since that version originally came out.
You can also use RC commands to turn on and off DEBUG logging on the mount and check what is going on, otherwise log will be pretty thin. Also note that SharePoint does not allow stream, so it means the backup file needs to be created and stored somewhere in your local system before upload can take place. Highly recommend you specify a path for it to be stored so you can handle the space accordingly. This is a limitation from Microsoft and not rclone as they require the exact size of the file before upload can take place. Also SharePoint has a limit filesize of 250GB, so you might need to either make smaller files or use the chunker backend to have rclone do it for you.
We are happy to help out, but please note you also need to be open to listen to suggestions and fixes and not only expect us to troubleshoot versions we stop using years ago and contain multiple issues that have been solved since.