I have had my galaxy S21 Ultra for a little over 2 years without any issues and just this week i went for swimming with the kids and got some splash of water on it and after some few hours the screen went dead. This isn't the first time to the swimming pool with the kids and phone having a splash of water over. It is supposedly water resistance to 1,5 meter and I never submerge it in water, so this is kind of strange to. The phone have no cracks whatsoever for water to even leak into the phone through the screen.
We're sorry to hear that you are experiencing problems with your Galaxy S21 Ultra.
In this case, we recommend that you turn off the phone and then put it in a room with normal room temperature and let it dry for 24 hours. See if it works normally after this. Should the problem still persist, we recommend that you take it in for service so that our technicians can examine it more closely. You can take it in for service through the retailer.