MongoDB container environment variables not applied for authentication

I'm running a MongoDB instance as a Windows container using Docker Compose, and I'm having trouble with MongoDB authentication. Although I’ve set the MONGO_INITDB_ROOT_USERNAME and MONGO_INITDB_ROOT_PASSWORD environment variables, MongoDB Compass fails authentication when I attempt to connect using these credentials. If I remove the username and password from the connection string in MongoDB Compass, I can connect without issues, which suggests the environment variables might not be applied correctly.

Docker Compose Configuration:

services:
  mongo:
    image: mongo
    restart: always
    ports:
      - 27017:27017
    environment:
      MONGO_INITDB_ROOT_USERNAME: root
      MONGO_INITDB_ROOT_PASSWORD: example

Steps to Reproduce:

1. Start the MongoDB container using the above Docker Compose configuration.
2. Try connecting with MongoDB Compass using the following credentials.
   • Username: root
   • Password: example

Expected Behavior:
The MongoDB container should start with the specified root username and password, allowing authentication via MongoDB Compass.

Actual Behavior:
MongoDB Compass fails to authenticate with the provided credentials. However, I can connect without authentication if I omit the username and password from the connection string.

Question:
Why are the environment variables not being applied to the MongoDB container for authentication?

Start by reproducing the Windows Docker Compose setup and inspecting the container's initialization behavior and connection details. No repository file or test is identified; the work is complete only once the authentication behavior and required configuration are established clearly enough to define a repository change.