New IPhone 12 -apps will not open

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)

If the apps are still downloading (can take awhile when transferring to a new device) then you may need to stop them and allow them to reinstall a few at a time. You can also delete each app and reinstall

Uninstall then reinstall them.