Apple says iOS 18 allows you to more easily turn the iPhone off

https://9to5mac.com/2024/06/13/forget-how-to-turn-off-your-iphone-ios-18-now-offers-a-dedicated-power-button/

One of the unfortunate results of the iPhone dropping the Home button is
that turning your device off became more complicated than before.

There's even an official support page to teach you how to do it.
https://support.apple.com/guide/iphone/turn-iphone-on-or-off-iph841379c3d/ios

On older iPhones, you could just hold down the side button to see the power
slider appear on screen. But in today's post-Home button era, the side
button is now used to invoke Siri instead, so you have to hold both the
side button and a volume button to power down.

That small change broke years of muscle memory and wrought confusion, so
much so that Apple is introducing a dedicated power button in iOS 18.