You can configure virtual replicas from the 3.10.0 extension version and above.
To configure Virtual Replica for Sorting, go to Stores > Configuration > Algolia Search > Instant Search Result Page > Use Virtual Replica.
When you switch to Virtual Replica, Algolia deletes the Standard Replica and creates a corresponding Virtual Replica index. Virtual Replica slightly increases the primary index’s size (less than 10 MB per million records), but they don’t affect the number of records. For more information, see What are virtual replicas?.
Please note that Virtual Replica is only available on Premium plans.