Unable to turn off my iPhone 7 after iOS 15.8.4 update

Make sure that you are doing the Forced Restart correctly.

Quickly press and release the UP button

Quickly press and release the DOWN button

Hold in the Side button for at least 20-25 seconds and ignore the "slider". Keep holding the Side button in until you see the Apple logo in the center of the screen. Then....release the Side button

If you have tried this a few times and it does not help, there is a hardware problem with the phone. Make an appointment with the Genius Bar or take the phone to an authorized Apple service shop.

You can find a list of authorized shops in your are using this link: Find Locations

Hello!

Force restart your iPhone, and then try turning it off again. Let us know how you make out. Thanks!

That iPhone 7 is likely starting to show its age.

Have you checked the Maximum Capacity of the battery? Settings > Battery > Battery Health

Replace the battery if the Max Cap is under 80%