[{"_id":{"$oid":"6395471f80495752e7208c63"},"elements":[{"name":"Alice","age":20},{"name":"Bob","age":21},{"name":"Charlie","age":23}]},{"_id":{"$oid":"6395486980495752e7208c67"},"elements":[{"name":"Alice","age":20},{"name":"Bob","age":21},{"name":"Bob","age":24}]}]

db.collection.find({elements:{$elemMatch:{name:"Bob"}},$expr:{$gte:[{$reduce:{input:"$elements",initialValue:0,in:{$sum:["$$value",{$cond:[{$eq:["$$this.name","Bob"]},1,0]}]}}},2]}})