Greetings,

According to the mongodb doc about $out stage (https://docs.mongodb.com/datalake/reference/pipeline/out/#-out) it is possible to define out stage composed with a document which contains fields different than db and coll.

However, in latest driver (4.2.3), it only allows to use $out stage with db and coll fields (if it is used as document). Here is the places I spotted for the error is thrown:

1. https://github.com/mongodb/mongo-java-driver/blob/0ce5c4f7977aa7a0a8a2b10b0f22477a8231dce5/driver-reactive-streams/src/main/com/mongodb/reactivestreams/client/internal/AggregatePublisherImpl.java#L209
2. https://github.com/mongodb/mongo-java-driver/blob/0ce5c4f7977aa7a0a8a2b10b0f22477a8231dce5/driver-sync/src/main/com/mongodb/client/internal/AggregateIterableImpl.java#L232

Please consider to support Atlas specific $out stage as given in the mongodb doc.

Best,