Samsung Galaxy S9 User Manual page 142

Apps and features
Pop-up view
1
Tap the Recents button to open the list of recently used apps.
2
Swipe upwards or downwards, tap and hold an app window, and then drag it to Drop
here for pop-up view.
The app screen will appear in the pop-up view.
Moving pop-up windows
To move a pop-up window, tap the window's toolbar and drag it to a new location.
142
Minimise the window.
Close the app.
Maximise the window.