d9-eql/web/themes/custom/eql/eql.theme

<?php
/*
	* @files
	* Theme Template Funtions
*/

// use Drupal\Core\Template\Attribute;
// use Drupal\Core\Link;
// use Drupal\Core\Url;


function eql_preprocess_node(&$variables){
  $node = &$variables['node'];
  $variables['attributes']['class'][] = 'node-type-' . $node->gettype();
  if($node->gettype() == "actualite") {
    $actu_type = $node->get('field_actu_type')->getString();
    $variables['attributes']['class'][] = 'actu-type-' . $actu_type;
  }
}