[{"_id":"4d54cff54364000000004331","t":ISODate("2021-07-10T00:00:01.000Z"),"data":{"a":222936,"b":4824}},{"_id":"4d54cff54364000000004332","t":ISODate("2021-07-10T00:00:02.000Z"),"data":{"a":223525,"b":4863}},{"_id":"4d54cff54364000000004333","t":ISODate("2021-07-10T00:00:03.000Z"),"data":{"a":223425,"b":4892}},{"_id":"4d54d0074364000000004334","t":ISODate("2021-07-10T00:00:04.000Z"),"data":{"a":223445,"b":4905}}]

db.collection.aggregate([{$match:{t:{$lte:ISODate("2021-07-10T00:00:04.454Z")},}},{$sort:{t:-1}},{$facet:{first:[{$limit:1}],second:[{$match:{t:{$lte:ISODate("2021-07-10T00:00:02.454Z")}}},{$limit:1}]}},{$project:{con:{"$concatArrays":["$first","$second"]}}},{$unwind:"$con"},{"$replaceRoot":{"newRoot":"$con"}}])