Stop Windows 10 Apps From Running in the Background

To see which apps have permission to run in the background

1. open the Start menu or Start screen and
2. select “Settings.
3. Click or tap the “Privacy” icon in the Settings window
4. Scroll down to the bottom of the list and select “Background apps
5.  You’ll see a list of apps that have permission to run in the background with an “On/Off” toggle.
6.  The default setting for each app is “On,” allowing each app to run in the background if it likes.
7. Set any apps you don’t want to run in the background to “Off.

Bear in mind that there’s a downside to this.
 If you prevent the Alarms app from running in the background, for example, any alarms you set won’t go off.