Database
[{_id:ObjectId("62464e3e75c6d843a338993b"),Name:"The Team",Members:[{User:NumberLong("699724278526580847"),Rank:3},{User:NumberLong("937398909418999808"),Rank:4},{User:NumberLong("829765893287562113"),Rank:1},{User:NumberLong("090119389582045756"),Rank:1},{User:NumberLong("772474927459011034"),Rank:1},]}]
Query
db.collection.aggregate([{$match:{Name:"The Team"}},{"$addFields":{"Members":{"$filter":{"input":"$Members","as":"m","cond":{$eq:["$$m.User",NumberLong("699724278526580847")]}}}}},{$unwind:"$Members"},{"$project":{Rank:"$Members.Rank",_id:0}}])