What will happen to my iPhone 16 Pro Max that slipped into water for 60 seconds?

Power off the phone if it is on and stand the phone on end leaning against a wall so the charging port is on the bottom. Give the phone at least 2 full days to dry out thoroughly.

Do NOT put the phone in rice.

Then, cross your fingers and power up the phone.

Hopefully, nothing, but do as Bob Timmons suggests. If it doesn't work correctly after a couple days, be prepared to buy a replacement iPhone. Water and electronics are mortal enemies and if the phone is damaged from it's unfortunate swim, Apple won't attempt to repair it and it will need to be replaced.