This page redirects to an external site: https://developer.wordpress.org/reference/hooks/widget_title/
Filter the widget title.
<?php apply_filters( 'widget_title', empty( $instance['title'] ) ? __( 'Pages' ) : $instance['title'], $instance, $this->id_base ); ?>
widget_title is located in wp-includes/default-widgets.php