This is covered in the User Management guide, but repeated here for consistency. To create the admin user, run the following command:
docker compose -f docker-compose.yml -f docker-compose.prod.yml run --rm django ./manage.py createsuperuser!!! warning Do not use upper-case characters when entering your email! If you do, you will not be able to log in.
If you are deploying for the first time, you can proceed to Finalizing Authentication Configuration.