>I think a button that is located behind the screen fits the definition of “hidden interface control” more so than a swipeable screen edge.

I couldn't disagree more.

A big physical button on the surface of the device that is both visible and touchable is completely unmissable. More importantly, it's unmistakably a control. There is simply no other explanation for its existence than being a control.

The edge of the screen on the other hand exists because the screen has to end somewhere. There is no hint whatsoever that it doubles as a control when touched in a certain way or that it doubles as multiple different controls when touched slightly differently.

That said, I'm not a dogmatic "UI physicalist" (if that's a thing). I hate the physical mute switch for instance and I'm not a huge fan of the physical double click to authorise purchases. And I don't want scrollbars constantly in my face.

I do believe that new ways of interacting with hardware can be introduced over time even if hidden. There's a legitimate trade-off beteween discoverability and productivity once you're familiar with the way a device works.

The problem is that some people really struggle with gestures even when they know they exist. I watched people fail to answer calls on Android because it required them to swipe up an on-screen icon.

The number of things you can do swiping or just touching somewhere near the bottom of the screen is staggering and constantly changing.