The app you are looking for is , developed by Eric Tsang (etsang) . It was specifically designed to restore the long-press shortcut for multi-window mode that was removed in newer Android versions. Download Options
: The safest way to install the Split Screen Shortcut app directly to your device. The app you are looking for is ,
: After installing, you must enable the app's Accessibility Service in your phone's settings for the shortcuts to work. The app you are looking for is ,
: Open the app to select which button (Home, Back, or Overview) will trigger the split-screen action. The app you are looking for is ,