There is little chance that the OS of your VM is supported. I recommend that you Move a Discourse site to another VPS with rsync, skipping the database files, build the new container and then restore a backup from the existing site.
Actually, I would probably recommend that you run a fresh discourse-setup rather than using your existing app.yml and copy over the SMTP settings and such. There have been some changes there too.
Pretending for a minute that you perform OS upgrades on the VM to get it up to date, there have also been at least two postgres upgrades since then. Trying to upgrade in place will not go well. If you try, and it fails, I won’t say “I told you so,” but I won’t say anything else, either.