I've never encounter drowned mob.. Normal zombie also never get drown after 3-5 minutes on water.
Comments 4
I think they released an incomplete version. Cuz you also cant summon them through commands, zombies dont convert and undead mobs no longer sink. Its like 1.2.20 content but with different version number. Rather annoying really.
Drowned are still behind experimental features toggle in Update Aquatic phase 1 (which is the current release build). Phase 2 should enable them fully along with Turtles and bubble columns.
As mentioned, some features are behind the Experimental Gameplay option, or are stil in beta testing. More information about what is included can be read about in the full changelog.
Drowned aren't spawning in my world either, on Xbox One