Dr Malik says:
Watch out for the iPhone 12. It has a circular magnet that might deactivate your implantable defibrillator.
This article says it can happen- if the phone is over the device- which is usually under the skin by our left shoulder.
Some FitBits and other devices have been described to do the same.
If you have a pacemaker or ICD, consult your Cardiologist before buying the latest – or at least keep the thing well away from your chest!