iPhone 12 Pro will not open apps and settings don’t open and will not shut down either

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) Force restart iPhone - Apple Support (IN)

Yes, you have already said that. Did you try a forced restart as i suggested?