I have a totally different experience. I accidentally submerged my iPhone X in the sea as I got off a boat[1]. The phone although supposedly considered waterproof went mental and basically stopped working. I was flying back via Singapore (a week later) and went into the apple store at the airport. They replaced the phone and got me back up and running before my flight back to London. I live and had bought the phone in the UK. They even had special versions of the UK phone for this scenario.

[1] I was in the Philippines and I was getting off a boat in shallow sea water. My phone was in the bottom pocket of my beach shorts, and I walked through the sea water for maybe two to three metres distance up to waist height depth. This should have been ok for the depth I went.

Their suspicion was that the outer seal had failed (even though it had always been in a case).