working combination - nginx proxy-manager config - nginxproxymanager.com for Raspberry Pi 4

config.json

{
  "database": {
    "engine": "mysql",
    "host": "db",
    "name": "npm",
    "user": "npm",
    "password": "npm",
    "port": 3306
  }
}

docker-compose.yml

version: "3"
services:
  app:
    image: jc21/nginx-proxy-manager:2
    restart: always
    ports:
      # Public HTTP Port:
      - '80:80'
      # Public HTTPS Port:
      - '443:443'
      # Admin Web Port:
      - '81:81'
    environment:
      # Uncomment this if IPv6 is not enabled on your host
      DISABLE_IPV6: 'true'
    volumes:
      # Make sure this config.json file exists as per instructions above:
      - ./config.json:/app/config/production.json
      - ./data:/data
      - ./letsencrypt:/etc/letsencrypt
    depends_on:
      - db
  db:
    image: webhippie/mariadb:latest
    restart: always
    environment:
      MARIADB_ROOT_PASSWORD: 'passw0rd'
      MARIADB_DATABASE: 'npm'
      MARIADB_USERNAME: 'npm'
      MARIADB_PASSWORD: 'npm'
    volumes:
      - ./data/mysql:/var/lib/mysql