I had the exact same issue with my XS Max. It started to flicker green after being in the water for a couple seconds, then completely shut off. I left it in rice for two days, which i thought was complete bullshit but somehow actually worked. The phone would turn on and function but the screen was still plagued by the green hue and constant flickering. I held it vertical and used a hairdryer for about ten minutes, and the phone began working again, excepting Face ID. None of my water sensors were triggered. I first tried contacting apple support but apparently water damage is not covered by warranty.