That doesn't exist in the models I've designed. Microservices still exist and they each do their requisite task, but different work is done by different actors in the actor cluster. Actors are still a fantastic way of handling concurrency, since they can each be treated as single-threaded tiny programs that only think about themselves, and so I've used them in that way.

The actor just won't exist elsewhere, but another microservice that happens to use actors might exist. It would be sent a web request or a message in queue or similar.