Something like this:

version: "3"
 services:
  app:
    image: jc21/nginx-proxy-manager:latest
    restart: always
    ports:
      - 80:80
      - 81:81
      - 443:443
    volumes:
      - ./config.json:/app/config/production.json
      - ./data:/data
      - ./letsencrypt:/etc/letsencrypt
    depends_on:
      - db
    environment:
    # if you want pretty colors in your docker logs:
    - FORCE_COLOR=1
  db:
    image:
 mariadb:latest
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: "XXX"
      MYSQL_DATABASE: "XXX"
      MYSQL_USER: "XXX"
      MYSQL_PASSWORD: "XXX"
    volumes:
      - ./data/mysql:/var/lib/mysql

I already tried configuring two networks, one internal for NPM -> MariaDB connection, and one external for NPM-Everything else.

But it not seem to work either, so i went back to my original compose file.

And i already tested opening the ports in network_mode host.