filter everything

Search filter add/remove/restrict

By default, the search field in FE plugin uses the WP search algorithms, it does search in the Post content, Title, Excerpt, and Woo product SKU.

If you want to extend it with the new entities or limit it only to certain ones, you need to write custom code that will extend this logic with the necessary conditions.

For this, you can use the default WP hook “posts_search” to apply the required conditions – https://developer.wordpress.org/reference/hooks/posts_search/ for the needed post type.

Also, you can study the FE plugin code and check how the SKU search was added (custom field).
Here is the SKU search code in case you can’t find it in the FE plugin (this is the code from the plugin as an example, not a code that gives what you are looking for):

    public function addSkuSearchSql( $search, $wp_query )
    {
        if( $wp_query->get('flrt_query_hash') || $wp_query->get('flrt_query_clone') ){

            if ( $wp_query->get('wc_query') === 'product_query' || $wp_query->get('post_type') === 'product' /* || $wp_query->get('post_type') === 'product_variation' */ ) {
                global $wpdb;

                $product_id = wc_get_product_id_by_sku( $wp_query->get('s') );
                if ( ! $product_id ) {
                    return $search;
                }

                $product = wc_get_product( $product_id );
                if ( $product->is_type( 'variation' ) ) {
                    $product_id = $product->get_parent_id();
                }

                $search = str_replace( 'AND (((', "AND (({$wpdb->posts}.ID IN (" . $product_id . ")) OR ((", $search );
                return $search;
            }

        }
        return $search;
    }
    add_filter( 'posts_search', [$this, 'addSkuSearchSql'], 10000, 2 );