Welcome Rami!
I apologize if I misunderstood something as I am more familiar with Google Cloud than I am familiar with AWS however based on the announced use cases on https://aws.amazon.com/opensearch-service/ I believe that the most likely use case that is sort of hard to find would be Google Cloud Search which could be used to search for internal documents.
Other than that here are some of the other applications that would cover what is announced in AWS such as:
Cloud Login (Real-time log analytics and observability)
Big Query (Vector database for search and generative AI)
RAG engine for vertex AI (Retrieval Augmented Generation (RAG) for generative AI applications)
If none of these services matches your needs I apologize and would appreciate a little more context, maybe I can still help!