Do you mean that new action button thingy above the volume controls? You can reassign to perform something else in the settings. Only a few options to choose from, but it's totally possible.

As for powering off, you can tap the ⏻ symbol in the upper right-hand side corner of the control center.

You can assign the action button to run a shortcut, which opens up thousands of possibilities for what it can do.

I find the shortcuts extremely powerful all over different parts of the system, but I wish the contours of what it can and can't do were less opaque. Feels like a lot of time-wasting trial and error to discover what is or isn't possible on an iPhone.

No they are talking about the new camera button on the same side as the power/siri button. Which is semi-ironic considering the volume buttons still work fine as camera buttons they just don’t also handle zoom (you can slide your finger on the button to adjust zoom). I honestly am more annoyed at the button than enjoy it, yet another button I accidentally press when I nearly drop my phone and now have the camera app open.

You have to long-press that icon, not just tap it. Granted, it enables lockdown too, which is what the physical button used to do. As other have pointed, you can also do that by long-pressing lock + volume up.

It is still ludicrous how Apple had to work around its own decision to not use the camera button for anything else, since allowing us to move Siri to the camera button would leave the lock button for the easy duress gesture it traditionally has been.

If you long press the lock button and volume increase at the same time you can turn the new iPhone off. I can’t imagine doing 5 clicks to do this!

Which is not great considering it's a gesture you're supposed to do in duress, and should be easily done blindly with one hand. At least for my hands, that's too complex of an incantation.

Back tap is an accessibility feature, not intended for general public use.

Accessibility features are intended for general public use and they should work.

Specially on Apple devices, where common customization features are tucked away in the Accessibility menu.

I use it all of the time! I actually love it but I use it for grayscale mode, nothing actually critical. And yeah it triggers randomly but I am never upset to be without color.