The default Download File popup is part of the Mendix platform/widget behavior, so its design and responsive layout have limited customization options.
For the mobile behavior, opening the file in a new tab is generally handled by the browser/OS. Mendix cannot reliably control whether a new tab or confirmation is shown for subsequent downloads.
If you need a consistent UI and clear feedback for multiple downloads, the recommended approach is to implement a custom download flow instead of relying on the default popup. For example, use a custom modal/page with your own responsive design and show a success message/toast after each download is triggered. This gives you full control over the user experience across desktop and mobile.