After searching the web I found out that I have to upgrade my ubuntu server 14.04.3 and ownCloud 8.0.4 in steps to the newest version.
I hope that you can tell me that it is possible to install a fresh 20.04 ubuntu server with ownCloud 10.7 and then copy the database from the old server to the new one.
Now. Is it possible to copy the database from 8.0.4 to a fresh installation with the version 10.7 on a new server?
I’d suggest to first upgrade ownCloud on the Ubuntu 14.04 machine to 8.0.16, then to 8.1.12, and then to 8.2.11 first. Then upgrade to 10.1 (!) which is the last version that supports php 5. You’ll find the required server packages there: https://owncloud.com/de/aeltere-versionen/#server
With 10.1 on the old server you may follow the instructions at the link you provided and upgrade to 10.7 on the new server.
Keep in mind, that php8 is not supported, so be sure to have your php packages downgraded to php 7.4.
We have problems with the old server.
We cant apt, we cant ping, we cant do anything with this old server.
We are lucky that SSH and owncloud are working.
It seems like we have to download the data from 1 user manualy, add a new user to the new installation and copy the files manualy to the new installation.
The other users are not important.
We tried to copy the data (sql database, data and config) to the new server. But while we tried to import (from the dump of the old server) the SQL data the owncloud installation of the new server was shot.
Now Im making a new fresh owncloud/ubuntu installation and we will copy the 1 necessary user manualy with the data.