Installing Drupal 9

Create a folder named mydrupal, access this folder, and run the command below:

cd mydrupal

composer create-project drupal-composer/drupal-project:9.x-dev public --no-interaction

This command creates a public folder and downloads the Drupal files to it. ( more info ).

To access the public folder, run the following commands:

vendor/bin/drush site:install

Follow the instructions to complete the installation of Drupal 9.

Installing the basic modules and creating the child theme

Access the public folder and execute the following commands:

composer require stephane888/formatage_models
composer require stephane888/theme_reference_wbu

formatage_models allows you to build templates based on Drupal layout logic and use those created by other modules.

theme_reference_wbu is a child of the wb-universe theme. This theme should not be used; it is only intended as an example. Go to /public/web/themes, create a custom folder, copy the theme_reference_wbu theme (contrib/theme_reference_wbu) to custom. Rename theme_reference_wbu (contained in custom) to mythemedrupal. Go to the mythemedrupal folder and run the following command.

./traitementHtml.sh

For the following question, write: 1
Then enter theme_reference_wbu and confirm.

Your child theme is now ready to use.

Installing the child theme and the formatting_models module:

vendor/bin/drush en formatage_models 
vendor/bin/drush then mythemedrupal

Then go to the configuration (/admin/appearance) to set mythemedrupal as the default theme.

Doc : Drupal local server