The author describes a shortcut with three iPhone side button. It also works well with the double- or triple-tap shortcut on the back of the device (in Accessibility settings, IIRC).

Is there a shortcut for switching to black and white and back on Android? I am a long-term Samsung user and this article intrigued me.

On Android 15+ you can set a colour correction quick tile that can be set to activate greyscale. A very quick search seems to say you can do the same on Samsung/OneUI