Actually, you might want to check out https://tailcall.run (Disclaimer: I am the core maintainer of the project) It's an open-source API Orchestrator, in other words "a Zapier for APIs". If you find it interesting, hit our discord channel to learn more about it.
With Tailcall, you could compose API over multiple any of the following formats REST, GraphQL, and GRPC APIs to create a unified API endpoint. This could also be any of the above. So you could expose a set of REST endpoints atop, multiple GRPC APIs, where you are not just doing basic translations, but also sophisticated data transformation that has business logic inside it.