[{_id:ObjectId("65708c6237b62067296a398f"),date:ISODate("2020-09-15T04:07:05.000Z"),description:"playstation",category:"miscellaneous",cost:499,users:[{username:"Giacomo",amount:499}]},{_id:ObjectId("6570950cecb7eb1b4b868409"),date:ISODate("2020-09-15T04:07:05.000Z"),description:"tennis court",category:"sport",cost:100,users:[{username:"prova",amount:50},{username:"Giacomo",amount:50}]},{_id:ObjectId("6570953aecb7eb1b4b86840a"),date:ISODate("2023-02-09T03:12:15.012Z"),description:"netflix subscription",category:"entertainment",cost:100,users:[{username:"prova",amount:10}]}]

db.collection.find({"users.username":"Giacomo",$expr:{$and:[{$eq:[{$year:"$date"},2020]},{$eq:[{$arrayElemAt:[["","january","february","march","april","may","june","july","august","september","october","november","december"],{$month:"$date"}]},"september"]}]}})