Open the app you want to keep full screen
Drag the app divider all the way to the left or right edge
Tap the multitasking button at the top of the app and choose Full Screen
Swipe down from the top of the split-screen app and close one app
Open Control Center and turn off Stage Manager if it is enabled
Go to Settings
Tap Home Screen & Multitasking
Tap Multitasking
Turn off Allow Multiple Apps
Restart the iPad if split screen still appears