It's part of Good Guardians & it's called Screen Curtain. You can't download it from the Galaxy Store, but you can download Good Guardians from apk mirror as well as the different Good Guardians modules.
It's not a backdoor thing. If you read the whole article from which you copied, it says that this feature is part of Samsung's Galaxy Labs Good Guardians (it's not built into One UI), which is not available for download in Canada. So if you want it you'll have to download it was instructed by RedDogRabbit.