adminEnqueue.php

<?php
add_action('admin_menu', 'add_manage_sites_menu');

function add_manage_sites_menu(){
        // Save the reference to the new menu page
        $adminPage = add_menu_page(
                'New My Sites',
                'New My Sites',
                'read',
                'manage_sites',
                'manage_sites_menu',
                '',
                3
         );
        
        // Load the JS conditionally using the new menu page name
        add_action( 'load-' . $adminPage, 'load_admin_js' );
}

// This function is only called when our plugin's page loads!
function load_admin_js(){
        // Unfortunately we can't just enqueue our scripts here - it's too early. 
        // So register against the proper action hook to do it
        add_action( 'admin_enqueue_scripts', 'enqueue_admin_js' );
}

function enqueue_admin_js(){
        // Enqueue our script
        wp_enqueue_script( 'some-js', PLUGIN_URL . 'js/some.js', array( 'jquery') );
        
        // Enqueue our CSS
        wp_enqueue_style( 'some-css', PLUGIN_URL . 'css/some.css' );
        
}