I have a test server running on a Synology NAS. I use the following docker-compose.yml:

version: '3.8'

services:

  postgres:
    container_name: odoo-postgres
    image: postgres:14.1-alpine
    networks:
      - web
    ports:
      - 5432:5432
    environment:
      POSTGRES_DB: postgres
      POSTGRES_USER: odoo
      POSTGRES_PASSWORD: secret
    volumes:
      - ./postgres-data:/var/lib/postgresql/data
    restart: always

  odoo:
    container_name: odoo
    image: odoo:15.0
    networks:
      - web
    environment:
      HOST: postgres
      USER: odoo
      PASSWORD: secret
    depends_on:
      - postgres
    ports:
      - 8069:8069
    volumes:
      - ./config:/etc/odoo
      - ./extra-addons:/mnt/extra-addons
      - ./data:/var/lib/odoo
    restart: always
    links:
      - postgres

networks:
  web:
    external: true
    name: web

Please make sure that you have configured /config/odoo.conf correctly and included your module in the addons_path:

[options]
addons_path = /usr/lib/python3/dist-packages/odoo/addons, /mnt/extra-addons
...

In Odoo you also have to 'Update App List' in the Apps module. This item is visible when you activate the developer mode under 'Settings'. For more information, you can also check out my blog post: https://jortdevreeze.com/blog/odoo-2/dock-stack-launch-odoo-deployment-with-docker-and-portainer-4

I hope this helps!

I've been using Odoo on Docker with Synology NAS for a while.
If you are using it behind the Synology reverse proxy (NGINX) for LetsEncrypt, I always follow the script below to lock it down further for better performance and security.

Synology Tweaks:
1. Login via SSH
2. Go to /usr/syno/share/nginx, make a backup copy of both gzip.mustache and HSTS.mustache
3. Edit gzip - Add the following lines to the bottom:
gzip_types text/css text/less text/plain text/xml application/xml application/json application/javascript;
gzip on;
4. Edit HSTS.mustache - Add the following:
add_header Strict-Transport-Security "max-age=15768000; includeSubdomains; preload" always;
add_header X-Frame-Options SAMEORIGIN;
add_header X-Content-Type-Options nosniff;
add_header Referrer-Policy "strict-origin";
add_header X-XSS-Protection "1; mode=block";
add_header 'Content-Security-Policy' 'upgrade-insecure-requests';
5. Run nginx -t, systemctl reload nginx, then systemctl restart nginx
6. Test via Gtmetrix, SSLTest and securityheaders.com

Ok that helps me, but that will be my problem, that the module is not correct in the odoo.conf. My problem, I just realized that I can't find / open it. I also looked at your blog. You install the Odoo via stack and I simply installed it via New Container. That's probably why I wasn't able to store the data correctly there.