Water exposure iPhone 6s
Rice may have worked on much older devices. The iPhone 4 and later have so small physical gaps, that if liquid gets past the liquid indicator sensors, you will need to desolder parts off the logic board and wash / repair the corrosion that happens in a matter of hours (worst case) or when drying (best case).


https://www.youtube.com/watch?v=wJr7Ts86wpk


Unless you need data off the device, it's best to get it to professional level repair or replace it when it fails to start like yours does now. Display problems indicate that power lines are shorted or corroded internally.