How stupid can a "smartphone" be if the one-handed swipe gesture doesn't automatically turn off when playing a mobile game? Seriously? How has absolutely nobody at samsung thought about doing this? Would be the easiest software fix in the world.
Have you tried creating a custom mode to do this in Modes and Routines? You can easily create one when you open a game or Gaming Hub the option to turn off One Hand Operation with one toggle flip. It's a neat option to allow folks the ability to customize OneUI to their liking for specific uses without totally bloating the OS with options only some need. Try it, very powerful tool for many different situations
