[{"_id":1,"actors":[{"matricule":"AVB","name":"XXX"},{"matricule":"AVB","name":"YYY"}]},{"_id":2,"actors":[{"matricule":"PMH","name":"FFF"},{"matricule":"BNG","name":"HHH"}]}]

db.collection.find({$expr:{$eq:[{"$arrayElemAt":["$actors.matricule",0]},{"$arrayElemAt":["$actors.matricule",1]}]}})