I had a bit of a scare last night updating the 14 Pro Max from 17.7 to 18.
At some point the screen was completely black and the phone did not respond to any buttons (neither the power button nor the soft reset button combo) for a couple of minutes (it looked completely dead, and there was no progress bar whatsoever, nor the Apple logo), only to wake up suddenly, without anything indicating the boot process, on the home screen.
I thought the install had failed because the phone had rebooted less than five minutes before and there was no logo and no progress bar, but it did install iOS 18. It felt strange as this was the quickest iOS install ever, but showing no signs of progress was scary (having read the reports of bricked iPads).