db={"profiles":[{"_id":ObjectId("6074338b2fed706fbf415fa3"),"videoURL":"video_url_1"},{"_id":ObjectId("6074338e2fed706fbf415fa4"),"videoURL":"video_url_2"},{"_id":ObjectId("6074338f2fed706fbf415fa5"),},{"_id":ObjectId("6074338f2fed706fbf415fa6"),"videoURL":"video_url_4"}],"users":[{"_id":ObjectId("607433be2fed706fbf415fa6"),"profile":ObjectId("6074338b2fed706fbf415fa3"),"following":[]},{"_id":ObjectId("607433cd2fed706fbf415fa7"),"profile":ObjectId("6074338e2fed706fbf415fa4"),"following":[ObjectId("607433be2fed706fbf415fa6"),ObjectId("607433e12fed706fbf415fa8"),ObjectId("607433e12fed706fbf415fa9")]},{"_id":ObjectId("607433e12fed706fbf415fa8"),"profile":ObjectId("6074338f2fed706fbf415fa5"),"following":[ObjectId("607433be2fed706fbf415fa6"),ObjectId("607433cd2fed706fbf415fa7")]},{"_id":ObjectId("607433e12fed706fbf415fa9"),"profile":ObjectId("6074338f2fed706fbf415fa6"),"following":[ObjectId("607433be2fed706fbf415fa6"),ObjectId("607433cd2fed706fbf415fa7")]}]}

db.users.aggregate([{$match:{_id:ObjectId("607433cd2fed706fbf415fa7")}},{$lookup:{from:"users",let:{following:"$following"},pipeline:[{$match:{$expr:{$in:["$_id","$$following"]}}},{$lookup:{from:"profiles",localField:"profile",foreignField:"_id",as:"profile"}},{$match:{"profile.videoURL":{$exists:true}}},{$project:{profile:{$arrayElemAt:["$profile",0]}}}],as:"following"}},{$addFields:{following:{$slice:["$following",0,2]}}}])