Database
[{"datetime":ISODate("2022-10-16")},{"datetime":ISODate("2022-10-17")},{"datetime":ISODate("2022-10-18")},{"datetime":ISODate("2022-10-19")},{"datetime":ISODate("2022-10-20")}]
Query
db.collection.aggregate([{$match:{datetime:{$gte:ISODate("2022-10-18"),$lte:ISODate("2022-10-19")}}},{"$unionWith":{"coll":"collection","pipeline":[{$match:{datetime:{$lt:ISODate("2022-10-18")}}},{$sort:{datetime:-1}},{$limit:1}]}},{"$unionWith":{"coll":"collection","pipeline":[{$match:{datetime:{$gt:ISODate("2022-10-19")}}},{$sort:{datetime:1}},{$limit:1}]}}])