Create a Drupal 9 Project using composer.

Using recommended-project template

composer create-project drupal/recommended-project my-project

For more information, see : https://www.drupal.org/docs/develop/using-composer/starting-a-site-using-drupal-composer-project-templates

And also

Get drupal8 using default Packagist.org (The composer packages repository) drupal repository.

composer create-project drupal/drupal drupal8

Few other repositories.

composer create-project drupal/drupal drupal8 --stability dev

composer create-project drupalcommerce/project-base drupal8 --stability dev

If you gave a private repository, You can use a package.json like:

{

    "package": {

        "name": "yourname/your-drupal-project",

        "version": "1.0.0",

        "dist": {

            "url": "https://your.domain/url-to/your-drupal-project.zip",

            "type": "zip"

        }

    }

}

Then:

composer create-project yourname/your-drupal-project drupal8 --stability dev --repository=packages.json

Tips:

Clear composer cache

composer clear-cache