Using Python multiprocessing.Process inside a Docker Container

The code below works when being run as a regular Python process. Calling start starts a new process.
When I run the same code inside a docker container, the method my_function never gets called.

from multiprocessing import Process

def my_function(x, y):
    print("process started")

def start():
    p = Process(target=my_function, args=(1, 2))

The Dockerfile has FROM python:3.8-slim-buster.
Is there some configuration needed on the Docker side to enable the multiprocessing?

Source: StackOverflow