It had never been opened. It fell in a pool. It stayed there about 30 seconds (1m deep). When I fished it out, screen was off and it never turned back on.

Sorry to hear that. It's an unusual outcome and strongly suggests the seal was somehow broken (or bent). How old was the phone?

https://youtu.be/Lv1kofMtpFs?si=CFUjQvrjHWDs3lFl