I created a fresh database and set up the kickstart file under a new domain (same host, just another domain), transfered the backup file to the directory of the new domain.
Started restoration and added the credentials of the new database into the script during the process.
After finishing the restoration of the website, I checked the backend - it shows the database credentials of the old database.
Also I had to re-enter some basic infos like website name, etc. I remember from previous restorations that this was not necessary.
The configuration file of the restored site -which shows credentials of old database - has 644 permission (also all other files)
I checked the new database - it was filled with data during the restoration.
Adding the new database credentials in the Joomla backend of the restored site was not a good idea, as the restored site is then not working at all.
I was repeating the restoration now 2 times, carefully looking, if I have missed something, but nothing I could identify to be set wrong. Also made a fresh backup and used that one.
As a site note: I am also using Admin Tools. So on the restored site, I re-created the .htaccess file (but I dont think this is relevant at all).
What am I missing? Thank you.