Thanks for surfacing the story about Backblaze.

I had the same type of thing happen to me with the LastPass leak, which made me very wary of closed-source supposed-e2e encrypted services.

Looking at Borg, it doesn't seem to have native support for the actual transfer of the remote backup. It seems like if I used Borg it would be for a local backup, and then I would need an additional layer to sync the backup to remote storage.

It looks like rclone does, mentioned in other comments here, any others?