Does Opensearch Serverless support delete-by-query?

For Opensearch Serverless, a collection is a logical grouping of one or more indexes that represent an analytics workload. Perhaps the action that you are trying to do can be found under the section Deleting Collections: https://docs.aws.amazon.com/opensearch-service/latest/developerguide/serverless-manage.html. Do note that deleting a collection deletes all data and indexes in the collection. You can't recover collections after you delete them.

Hope it helps!

The supported operations are listed here https://docs.aws.amazon.com/opensearch-service/latest/developerguide/serverless-genref.html#serverless-operations

There is no delete by query so I guess unfortunately no