[{"_id":1,"trailName":"Trail1","update":ISODate("2023-07-30T08:00:00Z"),"user":"Tom","comment":"xy"},{"_id":2,"trailName":"Trail1","update":ISODate("2023-07-31T08:00:00Z"),"user":"Mary","comment":"xy"},{"_id":3,"trailName":"Trail1","update":ISODate("2023-07-31T08:00:00Z"),"user":"Joe","comment":"xyz"},{"_id":4,"trailName":"Trail2","update":ISODate("2023-07-10T08:00:00Z"),"user":"Tom","comment":"xy"}]

db.collection.aggregate([{"$setWindowFields":{"partitionBy":"$trailName","sortBy":{"update":-1},"output":{"rank":{"$denseRank":{}}}}},{"$match":{"rank":1}},{"$group":{"_id":"$trailName","updateCount":{"$count":{}},"mostRecentUpdate":{"$max":"$update"},"users":{"$push":"$user"},"comments":{"$push":"$comment"}}}])