The Apps & features section of Settings in Windows 10 lists all installed apps as well as classic desktop programs. The section can be used to find out recently installed apps & programs, uninstall apps and programs, and reset apps.
When you perform a click on a desktop program entry under Apps & features section, Windows 10 displays Uninstall and Modify options. Likewise, when you click on a default app or an app installed from Store, you get Move and Uninstall options.
Many users often complain us that the Uninstall option or button is grayed out or is not clickable. This means that, at times, one cannot uninstall an app because the Uninstall option is grayed out.
Why uninstall button is grayed out in Settings?
You might have noticed this before, but not all users have observed that the Uninstall option is grayed out only for certain default apps, and not for third-party apps installed from Store.
Windows 10 doesn’t offer an option (at least, not yet) to uninstall certain native apps. That doesn’t mean that the Uninstall button or option is grayed out for all default apps. Only apps that are crucial to the operating system don’t show an Uninstall option in Settings. Alarms & Clock, Calculator, Camera, Mail and Calendar, Maps, Messaging, People, Photos, Store, Sticky Notes, Weather, Voice Recorder, and Xbox are some of the apps that you cannot uninstall via Settings.
If you are wondering how one has to remove these apps from Windows 10, you will glad to know that there are a couple of ways out there to remove these default apps. You can either use the PowerShell (see how to uninstall default Windows 10 apps) or popular tools like CClenaer to remove default apps (see three tools to remove default apps from Windows 10).
So, in short, the Uninstall option is not available for certain default Windows 10 apps. If you want to uninstall one these apps, please use above mentioned methods or tools.
Source