[ntoskrnl_exe]

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.

[gabeio]

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.

[ASalazarMX]

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.

[fizwidget]

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

[mzmzmzm]

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.