New installation: Can't create admin user

Environment:

  • unraid 6.11.1
  • mariadb (linuxserver)
  • nextcloud (linuxserver)

PROBLEM:
This is installation issue. After nextcloud docker install user needs to open nextcloud Web GUI to create new admin user and specify database connection parameters. When I do this, I get error that user can’t be created.
Is there a workaround for this problem? Is it possible to add admin user manually? And also is is possible to manually enter database connection parameters.

Thank you