Docker compose clone volume into src code

I have following simple docker-compose file:

version: "3.7"

services:
  db:
    image: postgres:12
    container_name: project-back_postgres
    environment:
      POSTGRES_PASSWORD: pass
      POSTGRES_USER: user
      POSTGRES_DB: project-back
    volumes:
      - type: bind
        source: ./db-data
        target: /var/lib/postgres/data
    ports:
      - "5432:5432"

My false expectation of this volume definition was, that volume will be available in folder db-data. However the folder db-data does not contain any volumes and remains empty.

How can I achieve this behavior that folder db-date contains volume of Postgres?