Split screen on Shield TV:
For the feature to work, you will need a keyboard connected to the device via Bluetooth or a wire. You have two ways to enable split-screen:
Press Windows + ^ (CMD + ^ on Mac keyboard) to run the current app on the right side. The previous app will run on the left side.
Press Windows + $ (CMD + $ on Mac keyboard) to run the current app on the right side. The previous app will run on the left side.
Android TV has one limitation that might prevent you from launching the split-screen mode—it can’t detect 3 keystrokes. So, to run applications in split-screen, you will need a keyboard which has dedicated ^ and $ buttons, as Android TV won’t allow you to use Windows/CMD, Shift, and $/^ at once.
Of course we need to find a workaround for this as all our windows English QWERTY keyboards don't have the dedicated $ and ^ characters but have 4 and 6 instead :(