Looks like it is VSCode itself, who occupies the 9003 port. And it is expected, since it listens for incoming connections.

The problem is that xdebug, running in container, cannot connect to VSCode, running on the host.

AFAIK 'host.docker.internal' does not work for linux (or WSL) by default. Please try to add these lines to your docker-compose (for 'web' container):

extra_hosts:
    - "host.docker.internal:host-gateway"

Please see this answer for details https://stackoverflow.com/a/67158212/6051839