Hi there. As you can see, last week I moved your post to a new thread as it wasn't related to the one you posted on. Also I started replying, but got sidetracked... Sorry about that.

Anyway, as you may have also seen, I've also approved your website account. Now that has been approved, if you log in, you can start a new forum thread yourself and/or add posts to an existing thread without waiting for me to approve it.

To your specific question/s, I'll start at the end and work backwards.

Unfortunately, we don't have any quick links, but I'm happy to give you "best effort" support via our forums here (in this thread is fine). I try to respond to post at least once per week. Often quicker, but as you've noticed, it's sometimes a little longer.

TurnKey servers that include MariaDB (fork of MySQL that remains mostly compatible). That shouldn't make any difference WRT Nextcloud and migrating your existing DB, but I thought it worth mentioning. All of our LAMP based appliances (in Nextcloud) have Adminer pre-installed (accessible via https on port 12322). All appliances also have Webmin (a web base admin UI) preinstalled (accessible via https on port 12321). Webmin is quite different to Plesk (which I'm not particularly familiar with), but should provide somewhat similar functionality.

Again, we don't have specific instructions for a manual Nextcloud data migration. But under the hood TurnKey is Debian. So any tutorial that covers a general Nextcloud migration from one Debian server to another should get you there. As Ubuntu is (mostly) based on Debian, following instructions for Ubuntu should also work.

Depending on how old your server is, then because of the different Nextcloud PHP requirements, you may need to do the upgrade/migration in a number of stages. I.e. update Nextcloud as far as possible, then either upgrade PHP on your current server (if possible) and upgrade Nextcloud some more. Our current appliances also come with a PHP version update/changing script - although only available via CLI (I'm a CLI guy! :). Also I forget which older PHP version are available (mostly it's used for accessing newer versions).

The only other specific thing that you may hit migrating your files to our Nextcloud app is that as per Nextcloud (security hardening) recommendation we use a separate data directory. If you have a particularly old Nextcloud version (before that was an option), or it just isn't installed like that, you will either need to leave your data directory within the Nextcloud root directory (easiest), or migrate that yourself (PITA AFAIK). I'm not a Nextcloud user myself so I can't help with that if you do want to migrate to the separate data dir but the NC forums have some info/recommendations.

I hope that gets you started, but as I say, if you hit any issues, please feel free to post back with questions, etc. If you do, please try to provide as much info as possible about changes you've made and any errors/issues you encounter.