[{"_id":{"$oid":"63ce93ffb6e06322db59fdc0"},"fruit":"apple","source":"tree","is_fruit_important":"true"},{"_id":{"$oid":"63ce93ffb6e06322db59fdc1"},"fruit":"orange","source":"tree","is_fruit_important":"true"},{"_id":{"$oid":"63ce93ffb6e06322db59fdc4"},"fruit":"mushroom","source":"dirt","is_fruit_important":"false"},{"_id":{"$oid":"63ce93ffb6e06322db59fdc5"},"fruit":"carrot","source":"dirt","is_fruit_important":"true"},]

db.collection.aggregate([{"$set":{"id":{"$toString":"$_id"}}},{"$unset":"_id"},{"$group":{"_id":"$source","objects":{"$push":"$$ROOT"},"source":{"$mergeObjects":{"source-of":"$source"}},}},{"$addFields":{"count":{"number_of_important_fruits":{"$size":{"$filter":{"input":"$objects","as":"object","cond":{"$eq":["true","$$object.is_fruit_important"]},}}},}}},{"$project":{"_id":0}}])