[{"_id":1,"streaks":[{"date":ISODate("2021-11-19T01:11:18.965Z"),"questionCount":0}]}]

db.collection.update({"_id":{"$eq":1}},[{"$set":{"new":{"$eq":[{"$filter":{"input":"$streaks","cond":{"$eq":[{"$dateTrunc":{"date":"$$NOW","unit":"day"}},{"$dateTrunc":{"date":"$$this.date","unit":"day"}}]}}},[]]}}},{"$set":{"streaks":{"$cond":["$new",{"$concatArrays":["$streaks",[{"date":"$$NOW","questionCount":1}]]},{"$map":{"input":"$streaks","in":{"$cond":[{"$eq":[{"$dateTrunc":{"date":"$$NOW","unit":"day"}},{"$dateTrunc":{"date":"$$this.date","unit":"day"}}]},{"$mergeObjects":["$$this",{"questionCount":{"$add":["$$this.questionCount",1]}}]},"$$this"]}}}]}}}])