How to access $menu variable in custom .PHP file that loads wp-load.php?

I have a file custom.php inside the WP root folder. My goal is to access the GLOBAL $menu variable that stores the admin menu items. In order to do that, I try loading the WordPress environment.

?php require $_SERVER['DOCUMENT_ROOT'].'/wp-load.php'; ?

After loading, I checked and made sure that the WordPress environment has been loaded.

if (defined('ABSPATH')) echo "WP Environment loaded."

Even when the wp-load.php is loaded, I am unable to access the global variable $menu which I can under a plugin file.

Is there any other file that needs to be loaded? Does the code after wp-load.php get executed after all the plugins were loaded?

Here is the whole code inside the file.

ROOT FOLDER
|__ customer (folder)
|   |_______test.php
|__ wp-admin
|__ wp-content
|__ ...

Here is what inside test.php

?php

    require $_SERVER['DOCUMENT_ROOT'].'/wp-load.php';
    global $menu;

    if (defined('ABSPATH')) {

        echo "WP Environment loaded.br";
        echo "Admin menu returns " .json_encode( $menu );
    }

?

And this is the output result:

WP Environment loaded.brAdmin menu returns null