Can an iPhone 12 Pro possibly survive in 5m / 16ft deep lake-water for 24 hours?
Yes hire a diver. The actual performance is designed to be better than the specifications, but drops and falls could allow cracks that make it soaked in minutes at 10cm.
Depending how air is trapped it could be just fine undisturbed for a day or three. You also can get data off a phone that isn’t safe to charge or run - don’t mess with rice and get it immediately to a recovery specialist if the value is in the data or continued operation of the device.