iPhone 15 stuck on installation screen during iOS 18.1 update

FYI, iOS 18.3.1 is the latest version.

Try a forced restart.

• Press and quickly release the volume up button

• Press and quickly release the volume down button

• Press and hold the side button.

• When the Apple logo appears, release the button.

Force restart iPhone - Apple Support (IN)

"iPhone 15 stuck on installation screen during iOS 18.1 update: Went to update my iphone 15 with IOS 18.1, my phone turned off, it went to the loading bar it just gets stuck on the installation page. Like I've waited 2 hours and no change. Please help"

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Fixing a Boot Loop:

Your iPhone is stuck in a Boot Loop. This typically occurs when you go about installing an update, and it stalled while in the process. Use my User Tip: How to Fix an iPhone in a Boot Loop - User Tip