Lock / unlock setting is missing iPhone 12 pro

I wonder if anyone has managed to resolve this yet? This is the setting that shuts off the iPhone when closing the case lid. My iPhone 11 Pro had the Lock / unlock setting under display and Brightness but it is missing with my new iPhone12. The curious thing is I gave my old iphone 11 to my wife and the option is now missing on her phone also, it the same case as I used when I had the phone so it must be something in her profile. I really miss this function and it saves on battery life too; so many posts and theories on google but still no resolution. It anyone knows the answer I would be very grateful