I changed my note 10 plus display and the new display had a pink square at the bottom with message saying "samsung retail mode isnt responding" and its not affecting the touch screen its just there and doesn't go
Enable developer options in Settings (Settings > About phone > Software information > Build number - Tap the Build Number option seven times until you see the message as developer mode is enabled. Return to the previous screen to find Developer options at the bottom.)
Find demo mode from the listing and see if enable demo mode option in toggled on, if it is on try to turn it off. Hope it might help
