¿Que contenedores docker utilizas?

version: '3'

services:
    db:
        image: postgres:latest 
        container_name: postgres 
#        ports:
#            - 5433:5432 
        restart: unless-stopped 
        volumes:
            - /volume1/docker/joplin:/var/lib/postgresql/data # Make database files persistent. Otherwise data is lost when the container is destroyed.
        environment:
            - APP_PORT=22300 # port joplin-server is reachable at
            - POSTGRES_PASSWORD=mipassword123 #  database password
            - POSTGRES_USER=admin #  database user
            - POSTGRES_DB=joplin #  database name
    app:
        image: joplin/server:latest
        depends_on:
            - db
        ports:
            - "22300:22300" # Expose internal port to LAN
        restart: unless-stopped
        environment:
            - APP_BASE_URL=http://IPDELNAS:22300 # <- HERE
            - DB_CLIENT=pg
            - POSTGRES_PASSWORD=mipassword123 
            - POSTGRES_DATABASE=joplin 
            - POSTGRES_USER=admin
            - POSTGRES_PORT=5432 
            - POSTGRES_HOST=db