My iPhone 7 (model A1778) does not prompt for a passcode before powering off

No iPhone prompts for a passcode before powering off. It is not a feature which is supported. And it wouldn't be a good feature. Requiring a passcode to power off could make it more difficult for users to reset their phones when they are stuck, and it could also pose challenges for users with accessibility issues.

iPhone has never prompted for a passcode before powering off ever before. There is also no reason for that as powering off an iPhone simply turns it off and back on to the Lock Screen, it does not access any personal information or data within the iPhone, which normally requires a passcode. The Require Passcode setting means that as soon as you lock your screen, your iPhone will immediately ask you to enter your passcode to unlock.

HafizSab wrote:

"My iPhone 7 (model A1778) does not prompt for a passcode before powering off, even though 'Require Passcode' is set to 'Immediately'."

That's correct. A passcode is not required to power it off. If it were, it would make basic troubleshooting virtually impossible.