add_filter( 'woocommerce_page_title', 'add_products_number_to_category_title', 99, 1 );
function add_products_number_to_category_title($title) {
if ( ! is_product_category() ) {
return $title;
}
$products_count = get_queried_object()->count;
return $title . ' (' . esc_html( $products_count ) . ')';
}