My iPhone 12 won’t power down. I can’t open anything

First thing to try is a forced restart:

* press and quickly release the Volume Up button.

* Press and quickly release the Volume Down button.

* Then press and hold the Side button until you see the Apple logo. (KEEP it pressed until the apple Logo appears)

If that doesn't clear it, see:

https://support.apple.com/en-gb/HT201412


And


https://support.apple.com/en-us/HT203899