Where can I see my PHP and DB version number ?

If you are looking for more information about your server or web application, you can find them under the Site Heath admin page /wp-admin/site-health.php?tab=debug in WordPress Admin

If you need to know your PHP version, you will be able to access it under the Server tab.

PHP Version

If you need to know your DB version, you will be able to access it under the Database tab.

DB Version