I see a couple of issues. When using docker, you should use the service name as the host. In your case, that would be ‘db’. So in your .env file, use:

DB_HOST=db

You’re exposing MySQL on port 3307, but the standard MySQL port is 3306. Change the MySQL port to 3306

db:
  ports:
    - 3306:3306
  expose:
    - "3306"

then in your .env file:

DB_PORT=3306

Use localhost as DB Host.

DB_CONNECTION=mysql
DB_HOST=localhost
# DB_HOST=db
DB_PORT=3307
DB_DATABASE=chat
DB_USERNAME=root
DB_PASSWORD=password

check container-id

docker container ls 

only first 4 characters required.

check logs using this command. Eg.

docker log a1bcd

Try

services:
  web:
    image: app-name:latest
    build:
      target: web
      context: .
    env_file:
      - .env
    ports:
      - "8000:80"
    volumes:
      - .:/var/www/html
    depends_on:
      - db
    networks:
      my_network:
        ipv4_address: 172.18.0.11

  db:
    image: mysql:8.0
    ports:
      - "3306:3306"
    expose:
      - "3306"
    cap_add:
      - SYS_NICE 
    command: --skip-grant-tables
    volumes:
      - ./cache/mysql:/var/lib/mysql
      - ./conf-mysql.cnf:/etc/mysql/conf.d/mysql.cnf
    environment:
      - MYSQL_ROOT_PASSWORD=root
      - MYSQL_DATABASE=chat
    restart: unless-stopped
    networks:
      my_network:
        ipv4_address: 172.18.0.10

networks:
  my_network:
    driver: bridge
    ipam:
      config:
        - subnet: 172.18.0.0/16

volumes:
  dbdata:

.env

DB_HOST=172.18.0.10
DB_PORT=3306