The behavior minecraft:behavior.defend_village_target is not listed in the entity components documentation included with the vanilla behavior pack for 1.16.0 through1.16.220. It was listed in the 1.14 documentation. Moreover, in the 1.16.220 iron_golem.json, minecraft:behavior.defend_village_target includes some parameters that are not listed in the 1.14 documentation.
Changed along with villagers that doesn't run around in their beds, MCPE-121894
Villagers behavior changed on 1.16.200 related to that issue