Minecraft wiki entry for Best_biomes_for_homes, associated text: Strays can spawn at night in the frozen ocean and deep frozen ocean, while polar bears spawn during day, which can be dangerous.
Underwater, these oceans are completely barren with neither kelp nor seagrass.
While being saved from drowned, unlike other oceans, frozen oceans also spawn regular hostile mobs, such as creepers, zombies, spiders, and witches (skeletons spawn in fewer rate). So strays are not the only hostile mobs found in here.
In Bedrock Edition, due to the surface in deep frozen ocean completely freezing, ocean monuments are less noticeable until the player gets mining fatigue, especially if the player travels on ice, even when the monument under feet due to surface landscape.
No dolphins spawn in the frozen ocean biome, which means if ruins or shipwrecks generate underwater, the player should find it manually or by fed dolphin from another ocean biome.