Starting from version 6, Mongo has server parameter allowDiskUseByDefault which is true by default. In Spring allowDiskUse for aggregation pipelines is false by default (because of using boolean) which means Spring always implicitly overrides Mongo default beheviour. Queries have no such issue. I think Spring should not set any parameters silently overriding Mongo default behaviour

public class AggregationOptions implements ReadConcernAware, ReadPreferenceAware {
...
private final boolean allowDiskUse;
...
}