How to Install Contributed D8 Module in D9 Using Composer?

Technical Solutions

Now that Drupal 8 (D8) support is over (link to the article), there are a lot of contributed D8 modules with patches in queue to make them work with Drupal 9 (D9) version. But there is a problem. You can’t composer require the module until you patch it and you can’t patch it before it is downloaded by Composer.

To solve this, Drupal. org has a lenient Composer endpoint that publishes all modules as D9 compatible whether it is or not. By using the lenient Composer endpoint you can composer require the module then use cweagans/composer-patches to apply the needed patch.

To know more: https://drupalize.me/tutorial/install-contributed-module-no-drupal-9-release?p=2766