PHP

wordpress admin url

<?php
  echo '<a href="' . esc_url( admin_url('nav-menus.php') ) . '">' . esc_html( 'Add Menu' ) . '</a>';
?>

wp site url link from admin

$url = site_url( '/secrets/', 'https' );
echo $url;
//Output: https://www.example.com/secrets/ or https://www.example.com/wordpress/secrets/

wp site url link from admin

$url = site_url( '/secrets/', 'https' );
echo $url;