How to define encrypted environment variable - not application platform

I have a droplet defined with Docker. I would like to define an environment variable (encrypted if possible). My docker-compose in the Postgres section uses commands such as - POSTGRES_USER=${POSTGRES_USER} The settings tab on the droplet has - what is it for = Service or API environment = staging. There is no setting option to add the environment variables. on my macBook I can set env variable using vi ~/.zshrc. If this cannot be done using the control panel is there a command line option to achieve this. Here is the section of the file .

The sql script defines the database name and schema used.

postgres:
    image: postgres:15.4
    _#command: postgres -c stats_temp_directory=/tmp_
    restart: always
    environment:
      - POSTGRES_USER=${POSTGRES_USER}
      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD}
      - POSTGRES_DB=${POSTGRES_DB}
      - POSTGRES_MULTIPLE_EXTENSIONS=${POSTGRES_MULTIPLE_EXTENSIONS:-postgis,hstore,postgis_topology}
    volumes:
      - ./postgres-data:/var/lib/postgresql/data
      - ./init.sql:/docker-entrypoint-initdb.d/init.sql
    ports:
      - 33066:5432