Looks like the latest MariaDB is not playing nice with Docker. It keeps on restarting, that’s why Firefly app can’t access it. This are the errors:

firefly_app-1 error:

getaddrinfo for db failed: Temporary failure in name resolution

firefly_db-1 error:

[Note] [Entrypoint]: Entrypoint script for MariaDB Server 1:10.9.2+maria~ubu2204 started.
[ERROR] [Entrypoint]: mariadbd failed while attempting to check config
        command was: mariadbd --verbose --help --log-bin-index=/tmp/tmp.UIQ7MFsJkX
        Can't initialize timers

Fix: use older version of Mariadb, in my example, 10.8.2

My docker-compose file:

version: '3.3'

services:
  app:
    image: fireflyiii/core:latest
    restart: always
    volumes:
      - firefly_iii_upload:/var/www/html/storage/upload
    env_file: stack.env
    ports:
      - 8080:8080
    depends_on:
      - db
  db:
    image: mariadb:10.8.2
    hostname: fireflyiiidb
    restart: always
    environment:
      - MYSQL_RANDOM_ROOT_PASSWORD=yes
      - MYSQL_USER=firefly
      - MYSQL_PASSWORD=secret_firefly_password
      - MYSQL_DATABASE=firefly
    volumes:
      - firefly_iii_db:/var/lib/mysql
volumes:
   firefly_iii_upload:
   firefly_iii_db: