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minecraft:out_of_control is an entity component: it goes in the components object of a custom mob, or in one of its component groups. A flag that marks the entity as out of control. Boats use it so the rider can't steer them, for example while on ice or bubble columns.
Example
Inside the components object of BP/entities/<name>.json (values are the defaults or placeholders):
BP/entities/<name>.json
{
"minecraft:out_of_control": {}
}