Migration from Owncloud 8.2.7 to Nextcloud (solved)

I want to migrate our Owncloud installation to nextcloud.
The installed version of Owncloud is 8.2.7.

As I did not find a 9.x version of nextcloud to download, i’ve tried to immediately update to nextcloud 10.0.1. I tried this deleting all the files and folders from the owncloud-folder, just leaving the config-folder. My data is stored outside the owncloud-folder.
The database schema for the apps was updated, but ended up in an Error:
Exception: files can’t be disabled

After looking here in the forum I found a link to the 9.x nextcloud files, so I replaced the nextcloud 10-files with the nextcloud 9.0.53 files.
Now the page tells me, that an apps update is necessary and offers me the possibility to start actualisation.
After that I end on the nextcloud actualisation?-page, but nothing seems to happen.

I finally switched back to my old 8.2.7 Owncloud-installation and found in my database in the appconfig-table under lastupdateresult the following entry:
{“version”:“8.2.8”,“versionstring”:“ownCloud 8.2.8”,“url”:“https://download.owncloud.org/community/owncloud-8.2.8.zip",“web”:"https://doc.owncloud.org/server/8.2/admin_manual/maintenance/upgrade.html”}

After updating Owncloud to 8.2.8 I tried again to migrate to Nextcloud 9.0.53. This time it worked (after turning of my client).

In case you have clients connected, it is better to put your setup into maintenance mode before you update/upgrade.