Database

[{"_id":ObjectId("60073749694fd4d81e4d677d"),"AlertSettingId":ObjectId("5ffddaaa0b1d2c30b191599a"),"CurrentStatus":"success","Evaluations":[{"EvaluatedAt":ISODate("2021-01-19T19:47:18.850Z"),"ReferenceValue":1.0,"Status":"success"},{"EvaluatedAt":ISODate("2021-01-19T19:52:16.423Z"),"ReferenceValue":1.0,"Status":"triggered"},{"EvaluatedAt":ISODate("2021-01-19T21:47:16.400Z"),"ReferenceValue":1.0,"Status":"success"}]},{"_id":ObjectId("60085ec60a264ce3829a6335"),"AlertSettingId":ObjectId("5ffddaaa0b1d2c30b191599a"),"CurrentStatus":"triggered","Evaluations":[{"EvaluatedAt":ISODate("2021-01-20T18:03:01.040Z"),"ReferenceValue":1.0,"Status":"noDataFound"},{"EvaluatedAt":ISODate("2021-01-20T22:04:43.983Z"),"ReferenceValue":1.0,"Status":"triggered"},{"EvaluatedAt":ISODate("2021-01-20T22:39:43.978Z"),"ReferenceValue":1.0,"Status":"triggered"},]},{"_id":ObjectId("60099092f7386972de3e8a05"),"AlertSettingId":ObjectId("5ffddaaa0b1d2c30b191599a"),"CurrentStatus":"success","Evaluations":[{"EvaluatedAt":ISODate("2021-01-21T14:32:48.697Z"),"ReferenceValue":1.0,"Status":"noDataFound"},{"EvaluatedAt":ISODate("2021-01-21T14:37:44.929Z"),"ReferenceValue":1.0,"Status":"triggered"},{"EvaluatedAt":ISODate("2021-01-21T14:42:44.928Z"),"ReferenceValue":1.0,"Status":"triggered"},{"EvaluatedAt":ISODate("2021-01-21T15:17:46.052Z"),"ReferenceValue":1.0,"Status":"success"}]}]

Query

db.collection.aggregate([{$addFields:{lastSent:{$let:{vars:{filtered:{$filter:{input:"$Evaluations",cond:{$eq:["$$this.Status","triggered"]}}},},in:{$max:"$$filtered.EvaluatedAt"}}}}},{$sort:{lastSent:1}},{$project:{lastSent:0}}])

Result