My understanding is that you have a set of core functionality that is entirely optional so you only run what you want and need. These features are defined at a high level like state management (persistence) or an event bus.

Dapr provides a unified API that sits on top of all this and allows you to swap out your event bus system from say Kafka to Google PubSub without any code changes.

But under the hood everything seems to operate via gRPC calls.

Edit: I just came across this link which puts together a solid explanation of what Dapr is and how it works https://thenewstack.io/how-microsofts-dapr-simplifies-develo...