Right. It ain’t.
Cloud sync as a backup solution is worthless in my opinion. (It is good for sync, and sync only.)
What you need to do is set Scrivener to generate zipped/time-stamped backups.
→ Options / Backups
And then you regularly upload these backups to the cloud, somewhere like Google Drive for e.g.
Anywhere really, as long as it is not a sync folder that remains live and vulnerable to user error or system crashes.
Once the backup is uploaded to the cloud, you just forget about it. You don’t do anything with it – unless it is needed for a recovery, if ever.
It has been part of my daily routine to upload a backup of my day’s work for years now : never once did I have a problem.
→ Have the backup function target a designated “in transition” folder on your desktop (or anywhere easily accessible to you). Backups will accumulate there (set the function to “Keep all backups”). And when finally you have time to upload (so to make a backup of those backups) you only need to do it for the pertinent ones. – Usually the most recent one per project.
After which you clean the folder. – In my case I duplicate the pertinent backups I just uploaded to Google Drive to an external hard-drive, then reset my backup folder by deleting everything from it.)
I explain it all in more details here: