D8 - Passing a PHP variable to JavaScript with drupalSettings

MODULE.libraries.yml

library:
  version: VERSION
  js:
    js/script.js: {}
  dependencies:
    - core/jquery
    - core/drupal
    - core/drupalSettings

MODULE.php

<?php

$build = [
  '#attached' => [
    'drupalSettings' => [
      'configPageStuff' => [
        'varX' => 123456
      ]
    ]
  ]
];

// or

$build['#attached']['drupalSettings']['configPageStuff']['varX'] = 123456;

script.js

(function($, Drupal, drupalSettings) {
  'use strict';

  Drupal.behaviors.moduleBehavior = {
    attach: function(context) {
      
      console.log( drupalSettings.configPageStuff.varX );
      
    }
  };

})(jQuery, Drupal, drupalSettings);

test.css

.this-is-a-test{
  color: orange;
}