Hi @Kwen,
since you want to migrate to a Zammad package install, what you need to do is, get your data out of your 2.9 docker-compose install and migrate that into a 2.9 package install.
From there, you’re going to have to follow a step-by-step upgrade path, going from major version to major version (never upgrade Zammad skipping over the next major version, ever). You’re most likely also going to have to upgrade your chosen distribution along the way, as packages for 2.9 won’t be available for the latest versions of (e.g.) Debian or Rocky, and packages for the current stable (6.3) aren’t available for old distros.
Our official documentation can be useful for you here (see links below), but please be aware of the fact that our current documentation is regarding current Zammad versions. Especially the backup/restore part might have to be performed manually, because the scripts may or may not work.
In any event, please have snapshots and backups so you can recover should something go awry during the process.
Good luck!
Links:
Zammad Docs: Install From Package
Zammad Docs: Backup and Restore
Zammad Docs: Updating Zammad