The iPhone Duo lacks the Action Button, but you can emulate it. Press and hold the lock screen to edit, tap Customize, replace the Camera icon with a control or Shortcut. Choose a specific action like a Focus Mode or run a Shortcut that does multiple things. When you pick up your iPhone, a single tap on that bottom right lock screen icon performs your chosen action. You could use the bottom left icon instead. By default the right icon opens the camera, but you can also swipe the lock screen or press the Camera Control button.
Shortcuts are better. Just like the real Action Button, running a Shortcut gives more benefit. One button can turn on the torch, switch on a Focus Mode, and run an app. Most usefully, one Shortcut can be a menu for any or all of your other Shortcuts. From iOS 27 onwards, it's easier than ever to tell your iPhone what to do: open the Shortcuts app, tap the plus sign, and write a sentence describing what you want.
This works well if you have few Shortcuts, but is a bad idea with hundreds. You can make a Shortcut that displays all your folder Shortcuts in a menu. One Shortcut can change based on your Wi-Fi network, offering different options.
There is nothing the Action Button does that you cannot replicate with a control or a Shortcut. But emulating a physical button with an on-screen one has limits. You won't be able to pick up your iPhone and press the button without looking. Since the iPhone Duo has no Action Button, this is the best you can do.
Source: AppleInsider · Summarized by HeadlinesBriefing