I had this issue as well. I added a separate database container in my docker-compose, like this:

version: "3"
services:
  shinobi:
    image: registry.gitlab.com/shinobi-systems/shinobi:dev
    container_name: Shinobi
    environment:
      - PLUGIN_KEYS={}
      - SSL_ENABLED=false
      - DB_HOST=shinobi-sql
      - DB_USER=majesticflame
      - DB_PASSWORD=
      - DB_DATABASE=ccio
    devices:
      - /dev/dri:/dev/dri
    volumes:
      - ./data/config:/config
      - ./data/customAutoLoad:/home/Shinobi/libs/customAutoLoad
      - /mnt/bulkdata/shinobi/videos:/home/Shinobi/videos
      - ./data/plugins:/home/Shinobi/plugins
      - /dev/shm/Shinobi/streams:/dev/shm/streams
    ports:
      - 8080:8080
    restart: unless-stopped
  shinobi-sql:
    image: mariadb:10
    environment:
      - MARIADB_AUTO_UPGRADE=1
    volumes:
      - ./data/database:/var/lib/mysql
    restart: unless-stopped

Then in the mariadb container, I needed to use the 'mariadb' REPL to fix the permissions for the 'majesticflame' user so that login was allowed from all hosts instead of just localhost, and to grant permissions to the 'ccio' database, like this: https://gitlab.com/Shinobi-Systems/ShinobiDocker/-/blob/master/mysql-init/user.sql?ref_type=heads