Why can’t istore technician fix my iPhone 12 Pro Max at a fee instead of telling me it’s water damaged that I should buy another one

You don't have to see any water for the phone to be water damaged. And there are sensors built into the phone, technicians can check and if they are tripped, the phone is unrepairable.

By the way, putting your iPhone in Rice likely made your problems even worse. It's an old wives tale that rice can dry out electronics. It can't. And rice dust gets in the charging port and causes further damage.

Water damaged iPhone's cannot be fixed, that's why. Apple Warranty doesn't cover liquid damage. The technician is correct in suggesting you need to buy a new iPhone. Sorry. Water and electronics are not good friends.

They don’t say that. They say it’s passed certification testing. Those are the parameters for the certification test. They are tested under controlled laboratory conditions. That does not translate to real world use for exposure to liquids.

No device. None, not watches, not electronics, nothing, should ever be submerged at all unless it’s rated to at least 50 Meters of water resistance.

I don’t understand how apple can say the iPhones are good for 30 minutes up to depths for 6 meters and not make good on it when it doesn’t hold up to that. Seems pretty ridiculous to me.