Linode内でのアップデート作業中に、データベースファイルがサーバーと互換性がない問題が発生

You can copy the backup with scp/rsync. It’s easier and faster (unless you don’t know what that means).

You really want to create a new VM with a new OS (not a backup of a server with an out-of-date os) and move to it as described at Move a Discourse site to another VPS with rsync. The one that I just copied also had some ownership issues. You probably will too.

If discbak is running the same image as the other server, I’d expect it to give you a certificate error (unless you visited http://) and then redirect to whatever is in HOSTNAME.