Database
[{"uID":"12345678","midNightTimeStamp":NumberInt(1645381800),/** 21st Feb 2022 midnight IST*/"energyConsumed":NumberInt(53)},{"uID":"12345678","midNightTimeStamp":NumberInt(1645641000),/** 24th Feb 2022 midnight IST*/"energyConsumed":NumberInt(30)}]
Query
db.collection.aggregate([{$group:{_id:{$dateToString:{format:"%Y-%m",date:{$toDate:{"$multiply":["$midNightTimeStamp",1000]}}}},monthlyConsumption:{$sum:"$energyConsumed"}}}])