Permission error right after creating docker volumes

Question

I have a docker compose for a nextcloud instance, using mariadb on a debian 12.

My dockercompose :

networks:
  mywebsite_nextcloud_network:
    external: true

services:
  db:
    image: mariadb:10.6
    container_name: mywebsite.fr-nextcloud-db
    restart: always
    command: --transaction-isolation=READ-COMMITTED --log-bin=binlog --binlog-format=ROW
    networks:
      - mywebsite_nextcloud_network
    volumes:
      - ./data-db:/var/lib/mysql
    environment:
      - MYSQL_ROOT_PASSWORD=$NEXTCLOUD_MYSQL_PASSWORD
      - MYSQL_PASSWORD=$NEXTCLOUD_MYSQL_PASSWORD
      - MYSQL_DATABASE=nextcloud
      - MYSQL_USER=nextcloud

  mywebsite.fr-nextcloud-app:
    container_name: mywebsite.fr-nextcloud-app
    image: nextcloud
    restart: always
    networks:
      - mywebsite_nextcloud_network
    ports:
      - $NEXTCLOUD_PORT:80
    links:
      - db
    volumes:
      - ./config/:/var/www/html
      - ./data-nextcloud:/var/www/html/data
    environment:
      - MYSQL_PASSWORD=$NEXTCLOUD_MYSQL_PASSWORD
      - MYSQL_DATABASE=nextcloud
      - MYSQL_USER=nextcloud
      - MYSQL_HOST=db

BEFORE starting docker, the three volumes ('./data-db', './data-nextcloud', './config/') DON'T exists.

After running docker compose up, My maria/Mysql Don't want to init, it says mkdir: cannot create directory ‘/var/lib/mysql/’: File exists BUT all 3 volumes are created next to my docker-compose.yml :

root@homeserver:/data/apps/mywebsite.fr/nextcloud# ll
drwxr-xr-x 16 www-data www-data        4,0K 16 janv. 22:19 config
drwxr-xr-x  2      999 systemd-journal 4,0K 16 janv. 22:28 data-db
drwxr-xr-x  2 root     root            4,0K 16 janv. 22:28 data-nextcloud
-rw-r--r--  1 root     root             978 16 janv. 22:28 docker-compose.yml
-rw-r--r--  1 root     root             190  7 janv.  2024 .env

My "config" have been initialized:

root@homeserver:/data/apps/mywebsite.fr/nextcloud# ll config
total 1,3M
drwxr-xr-x 16 www-data www-data 4,0K 16 janv. 22:19 .
drwxr-xr-x  8 ilian    ilian    4,0K 16 janv. 22:39 ..
drwxr-xr-x 42 www-data www-data 4,0K 16 janv. 22:18 3rdparty
drwxr-xr-x 54 www-data www-data 4,0K 16 janv. 22:19 apps
-rw-r--r--  1 www-data www-data  26K 16 janv. 22:18 AUTHORS
-rw-r--r--  1 www-data www-data 2,1K 16 janv. 22:18 composer.json
-rw-r--r--  1 www-data www-data 3,4K 16 janv. 22:18 composer.lock
drwxr-xr-x  2 www-data www-data 4,0K 16 janv. 22:19 config
-rw-r--r--  1 www-data www-data 3,8K 16 janv. 22:18 console.php
-rw-r--r--  1 www-data www-data  34K 16 janv. 22:18 COPYING
drwxr-xr-x 24 www-data www-data 4,0K 16 janv. 22:19 core
-rw-r--r--  1 www-data www-data 7,4K 16 janv. 22:18 cron.php
drwxr-xr-x  2 www-data www-data 4,0K 16 janv. 22:19 custom_apps
drwxr-xr-x  2 root     root     4,0K 16 janv. 22:18 data
drwxr-xr-x  2 www-data www-data  20K 16 janv. 22:19 dist
...

But both data-db (sql) & data-nextcloud are empty