Note app cloud backups

I'm using a Onyx boox Max2.

I did a cloud backup in the Note application, and can see it when I go to the backup and restore screen in the Note application, but:

1. I don't seem to be able to delete the cloud backup.
2. I have no idea *where* this backup is. I had assumed it would use my Google drive, since I'm signed into google on the device, but it's not there. Is this some cloud service Onyx are providing? If so, how is it authenticated? device ID? secret stored on device? I really hope it's secure. How much storage is available?

More genereally, I'd like an automatic way of getting files on the device backed up to my own servers, for possible pulling apart and rendering (and of course, backing up). Does anyone have anything like that set up? something involving root and syncthing, perhaps...

Any ideas?