To initialize an Adobe Commerce 2 application in a sample sandbox script, execute the following script from the Adobe Commerce root directory:
<?php
error_reporting(E_ALL | E_STRICT);
ini_set('display_errors', 1);
require __DIR__ . '/app/bootstrap.php';
$bootstrap = \Magento\Framework\App\Bootstrap::create(BP, $_SERVER);
$objectManager = $bootstrap->getObjectManager();
//$model = $objectManager->get('Vendor\Module\Some\Model');