To comply with the Uninstall Policy 10.2.7 of the Microsoft Store, you need to ensure that your application can be easily removed by the user through a clear method of uninstallation. While you have mentioned that a shortcut is placed on the Desktop for users to easily uninstall the app, it seems like that alone is not sufficient to meet the store's requirements.
One option you can consider is to create an entry for your application in the Windows Add/Remove Programs list. You can do this by using the Windows Installer technology to install your application, which will automatically create an entry in the Add/Remove Programs list. Another option is to programmatically register your application in the Add/Remove Programs list during installation, as you mentioned. However, it's important to note that modifying the Windows Registry requires administrator privileges, and it's not guaranteed that your application will be run with admin privileges during installation from the Microsoft Store.
To communicate the command-line argument for uninstallation, you can add a "Uninstall Instructions" section to your app's store listing. This can include the command-line argument as well as any other necessary instructions for uninstallation.
Overall, it's important to ensure that your app complies with all of the Microsoft Store's policies before submitting it for review. This can help to ensure a smoother review process and increase the likelihood of your app being accepted for distribution on the Store.