You can list the deployed versions of an App Engine application using the Google Cloud Console and CLI commands. Here are the detailed steps for each approach:

1. Google Cloud Console:
   a. Go to the GCP Console: https://console.cloud.google.com/
   b. Select your project.
   c. Navigate to the App Engine dashboard by clicking the hamburger menu, then click on “App Engine.”
   d. Click on the “Versions” tab on the left side menu.
   e. You will see a list of deployed versions for your App Engine application.
2. CLI Commands (gcloud):
   a. Install and set up the Google Cloud SDK: https://cloud.google.com/sdk/docs/install
   b. Authenticate with your GCP account: gcloud auth login
   c. Set the active project: gcloud config set project PROJECT_ID
   d. List the deployed versions: gcloud app versions list

The output will display the list of deployed versions, including their IDs, status (serving/stopped), traffic allocation, and other details.

Terraform does not provide a direct way to list the deployed versions of an App Engine application. Terraform is primarily used for infrastructure management and deployment, not for querying the state of deployed applications. You should use the Google Cloud Console or gcloud CLI commands to list the deployed versions.