DemoteNode.php

<?php

namespace Drupal\node\Plugin\Action;

use Drupal\Core\Action\Attribute\Action;
use Drupal\Core\Field\FieldUpdateActionBase;
use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\node\NodeInterface;

/**
 * Demotes a node.
 */
class DemoteNode extends FieldUpdateActionBase {
    
    /**
     * {@inheritdoc}
     */
    protected function getFieldsToUpdate() {
        return [
            'promote' => NodeInterface::NOT_PROMOTED,
        ];
    }

}