On a first time install I got the following exception message:
The configuration directory in settings.php is specified as './files/config_5e1fc1de8522994ae8943138b9f3a594/active', but this directory is either empty or missing crucial files. Check that the $config_directories variable is correct in settings.php.
I don't know, what to do.
The database is not yet created, the database user has full permissions, the owner of the files is www-data:www-data, the permissions are set recursively to 0777.
On the same system a Drupal9 and a typo3 installation are running without problems.
I will answer myself:
Create the database manually first.
This solves the problem.