Invulnerable

Invulnerable makes the targeted entity invulnerable to all damage, except damage from a creative mode player, or the void.

Using the invulnerable tag

Any non-player entity that has the entity-data tag, will be able to use the invulnerable tag.

To summon an entity with the invulnerable tag:
/summon villager ~ ~ ~ {Tags:["entity-data","invulnerable"]}

Tag	Command
invulnerable	data modify entity @t Invulnerable set value 1b