Add this to the active theme’s functions.php.

/**
 * Remove Website From Comments Form
 *
 * @since 	1.0
 * @refer	https://millionclues.com/wordpress-tips/remove-websiteurl-from-wordpress-comment-form/
 */
function mc_disable_comment_url ($fields) {
  unset($fields['url']);
  return $fields;
}
add_filter('comment_form_default_fields','mc_disable_comment_url');