The drowned should swim but they just 'walk' underwater and theyre really slow, almost useless they cant even attack you anymore. They should be able to swim like before and also the spawnrate of them is kinda low, i barely see them in the ocean, i only see them at ruined structures and it makes the rest of the ocean empty when you see just 1 drowned and another thing not related to this one, but mob spawners are impossible to find.