[{_id:1,"likes":{"likes":5,"users":["user1","user2","user3","user4","user5"]}}]

db.collection.aggregate([{$match:{"likes.users":{$in:["user1","user2"]}}},{"$addFields":{"afterRemoval":{"$setDifference":["$likes.users",["user1","user2"]]}}},{"$addFields":{"afterRemovalCount":{$size:"$afterRemoval"}}},{"$project":{"likes":{likes:"$afterRemovalCount",users:"$afterRemoval"}}},{"$merge":{"into":"collection","on":"_id","whenMatched":"replace","whenNotMatched":"discard"}}])