Xiaomi How to Allow/Deny Display over other apps

Facebook's Messenger or our Messages app is a good example of "Show over other apps". Under MIUI, this feature is called "Display Pop-up windows while running in the background.

In this case, the app on the Xiaomi smartphone has the authorization to show itself over other apps. In which form depends on the app itself. Apps can show themselves over other apps with a small pop-up, a video player, or as mentioned in the example, a round circle with profile photos of the individual Facebook chats.

Note: This permission is only visible when it is requested by an app.