[{"_id":1,"project":"project1","env":"dev","timestamp":1644515845},{"_id":2,"project":"project1","env":"dev","timestamp":1644519211},{"_id":3,"project":"project1","env":"qa","timestamp":1644515542},{"_id":4,"project":"project2","env":"dev","timestamp":1644513692},{"_id":5,"project":"project2","env":"qa","timestamp":1644514822},]

db.collection.aggregate([{"$sort":{"timestamp":-1}},{"$group":{"_id":{"env":"$env","project":"$project"},"doc":{"$first":"$$ROOT"}}}])