Thanks. Yes, the mountpoint is mounted. I was ssh-ed into it at the time of trying.
Yes, it is a DigitalOcean volume. I didn't copy the content to Hostinger. It wasn't clear to me what was needed; the docs didn't say anything about this situation, so I assumed that the Backup Config data would take care of it all.
But if not, can you suggest an approach for how to help the new Cloudron installation access the old data? I'd be happy to upload the backup manually but don't see a way to do that.