docker: drupal site doesnt survive a restart

Hello,

i use this docker image to run a container from: https://hub.docker.com/_/drupal
i have then run this command: docker run --rm drupal tar -cC /var/www/html/sites . | tar -xC /path/on/host/sites and mounted it as /var/www/html/sites

However, when the container gets restarted, it shows the installation page instead of the site with its content.

Does anyone know what i do wrong? I would expect the site returns to its normal status as there's site specific data in the sites folder thats beeing mounted.

here is my docker-compose file for completeness:

 version: '3'

services:

  drupal:
    container_name: <CONTAINERNAME>
    image: drupal:9.3-php8.0
    ports:
      - 8081:80
    volumes:
      - ./modules:/var/www/html/modules
      - ./profiles:/var/www/html/profiles
      - ./themes:/var/www/html/themes
      - ./sites:/var/www/html/sites
    restart: always
    networks:
      - drupal-network

  postgres:
    image: postgres:11
    container_name: <CONTAINERNAME>
    environment:
      POSTGRES_PASSWORD: <PASSWORD>
      POSTGRES_DB: drupal
      POSTGRES_USER: drupal
    restart: always
    networks:
      - drupal-network

networks:
    default:
        driver: bridge
    drupal-network:
        external: true

## EXECUTE THIS COMMAND FIRST: docker run --rm -v /opt/docker/drupal/sites:/temporary/sites drupal cp -aRT /var/www/html/sites /temporary/sites

Start with the provided docker-compose configuration and the commands used to copy and mount /var/www/html/sites. Check how the Drupal and PostgreSQL containers handle their data across a restart. Done means the existing site and its content return after restarting the containers instead of showing the installation page.