[{_id:1,title:"Task 1",assignedTo:["userId1","userId2","userId3"],status:"To do"},{_id:2,title:"Task 2",assignedTo:["userId1","userId2"],status:"In progress"},{_id:3,title:"Task 3",assignedTo:["userId3"],status:"Completed"}]

db.collection.aggregate([{"$group":{"_id":{status:"$status"},tasks:{"$push":{$cond:[{"$in":["userId1","$assignedTo"]},{_id:"$_id",title:"$title",assignedTo:"$assignedTo"},"$$REMOVE"]}}}},{"$project":{status:"$_id.status",tasks:1,_id:0}}])