WPtoMeiliSearch.php

//include( plugin_dir_path( __FILE__ ) . 'vendor/autoload.php');
//use MeiliSearch\Client;

// ^ in your class

    public function buildIndex(){
        $client = new Client('http://127.0.0.1:7700');

        $args = array(
          'posts_per_page' => -1,
          'post_status' => 'publish',
          'post_type' => 'event'
        );
        $posts = new WP_Query($args);

        $count = $posts->found_posts;

        $posts = $posts->get_posts();

        # An index is where the documents are stored.
        $index = $client->index('event');
        $allPosts = [];

        foreach( $this->genLoop($posts) as $post ) {
           
            $postArray = (array) $post;

            $postMeta = get_post_meta($post->ID);
            foreach ($postMeta as $key => $value) {

                    if(is_serialized(current($value))){
                        $postArray[$key] = unserialize(current($value));
                    } else {
                        if (DateTime::createFromFormat('Y-m-d H:i:s',current($value)) !== false) {
                            $postArray[$key] = (int) strtotime(current($value));
                        } else {
                            $postArray[$key] = current($value);
                        }

                    }
                }

            $allPosts[] = $postArray;
        }
       
        $add = $index->addDocuments($allPosts);
    }

    //generator
    protected function genLoop($posts){

         foreach ($posts as $post) {
             yield $post;
         }
    }