WP Frontend Admin displays the content in the frontend in the same way as the backend.
This means that if the backend page looks good on mobile devices, it will look good in the frontend as well.
The standard pages in wp-admin look good on mobile devices, and the pages added by other plugins might look good as well but some might not look good.
That totally depends on the plugin that created the backend page and not on WP Frontend Admin.
For example, hypothetically, the WooCommerce pages look good in mobile devices in the backend and the frontend. But if a specific WooCommerce doesn’t look good in the frontend dashboard when viewed in a mobile device, that would be an error in WooCommerce and not an error in our plugin. You could contact WooCommerce and ask them to add mobile support for that specific page.