StarterKit.php

<?php

namespace Drupal\starterkit_theme;

use Drupal\Component\Serialization\Yaml;
use Drupal\Core\Theme\StarterKitInterface;
final class StarterKit implements StarterKitInterface {
    
    /**
     * {@inheritdoc}
     */
    public static function postProcess(string $working_dir, string $machine_name, string $theme_name) : void {
        $info_file = "{$working_dir}/{$machine_name}.info.yml";
        $info = Yaml::decode(file_get_contents($info_file));
        unset($info['hidden']);
        file_put_contents($info_file, Yaml::encode($info));
    }

}