To help protect your PC and keep it running smoothly, Microsoft recommends only installing apps from the Microsoft Store. You can choose where you can get apps from and if you want to see app recommendations when you try to install an app from outside of the Microsoft Store.
Select Start > Settings > Apps > Apps & features.
Under Installing apps, select one of the available options. To stop seeing app recommendations, select either Allow apps from anywhere or Turn off app recommendations (options vary by Windows version).