need to change page title for order-pay

Use this hook:
add_filter( 'the_title', array($this, 'change_pay_for_order_title'), 10, 2);

This is an example function to change the title:

function change_pay_for_order_title($title, $id) {
	if(is_checkout_pay_page() && get_the_ID() === $id) {
		$title = "Pay for something other than Order";
	}
	return $title;
}

Found similar answer for thankyou page here: https://www.barrykooij.com/change-woocommerce-thank-page-title/