ideclonOriginal post
Rank 5: Hypervisor
This doesn't seem to be an option at the moment. Here's a Discussion and an open Issue on Github requesting this functionality.
Summary
Solution: There is currently no distinct functionality available in the app. However, a recommended approach is to maintain a metadata collection and update it with every document event. This way, you can fetch the metadata collection/document to get unique values. There is an ongoing discussion and open issue on Github regarding this feature request.