Database
[{"_id":ObjectId("61435ceb233ce0118c1d93ec")},{"_id":ObjectId("61435cf29598d31c17f0d839")},{"_id":ObjectId("611e5cf953396d78985d222f")},{"_id":ObjectId("61435cf773b8b06c848af83e")},{"_id":ObjectId("61435cfd7ac204efa857e7ce")},{"_id":ObjectId("611e5cf953396d78985d2237")}]
Query
db.collection.aggregate([{"$group":{"_id":null,"ids":{"$push":"$_id"}}},{"$unset":"_id"}])