How can I create a recommended project in the root directory?

If wwwroot is empty you can simply run the following command from inside this directory.

composer create-project drupal/recommended-project .

The . at the end says: current directory.

In some shared hosting platforms, you cannot change the root folder.

You have an optional "drupal/legacy-project" option that creates the legacy folder organization.

“composer create-project drupal/legacy-project wwwroot”

https://www.drupal.org/docs/develop/using-composer/starting-a-site-using-drupal-composer-project-templates

I have some websites on gandi.net (fr) shared hosting and it defaults the root folder to "subdomain.domain.tld/htdocs".

• I run the "drupal/recommended-project" composer command
• Rename the “web” folder to “htdocs”
• Edit the composer.json file to replace “web/” by “htdocs/”
• Run “composer update”

And voilá.

In the end, the “subdomain.domain.tld” folder looks like this:

• config/sync/ (created manually, outside of the Drupal installation directory, defined in settings.php)
• htdocs/
• private/ (created manually, outside of the Drupal installation directory, defined in settings.php)
• vendor/
• composer.json
• composer.lock

Edit: If you are unable to run the composer command in your shared hosting, do it locally on a LAMP (or Acquia Dev Desktop) and upload the compressed archive to your host.