Database
[{created_at:ISODate("2020-05-08T18:46:08.020Z"),view:true,cta:false},{created_at:ISODate("2020-05-08T19:00:00.020Z"),view:true,cta:true},{created_at:ISODate("2020-05-08T19:30:45.020Z"),view:true,cta:false},{created_at:ISODate("2020-05-08T19:55:50.020Z"),view:true,cta:true}]
Query
db.collection.aggregate([{$group:{_id:{hour:{$hour:"$created_at"}},count:{$sum:1},ctaCount:{$sum:{$cond:["$cta",1,0]}}}}])