When you request a let's encrypt wildcard certificate with virtualmin you may have an error like this:

Syntax:

\Drupal::service('page_cache_kill_switch')->trigger();

Example on a controller:

Install via composer

composer global require drush/drush:10.x

Install Apache 2 server

sudo apt install apache2

Install MySQL Server

sudo apt install mysql-server

Create a Drupal 9 project with composer