Actor systems differ in their means of communication. While actor systems use the actors as the main units that you connect, with fire and forget messaging to each actor's inbox, FBP proposes communication between named ports over channels with bounded buffers, very much like the CSP implementation in Go (just that you have long running components as in actor systems - something that can easily be implemented in Go with structs with go channels in fields for the ports, as shown in the FlowBase library I mentioned in another comment).

The FBP model provides implicit backpressure, because of the bounded buffers on the channels. The actor model on the other hand is more loosely coupled and flexible.

This actually means FBP systems are slightly more optimal for efficient within-one-node, in-memory parallellisation, whereas actor systems shine more for distributed systems.

They shine on different scales, in other words.

I wrote a post many years ago on this, that seems to have aligned with the experience of a number of people, based on the reactions in the comments: https://rillabs.com/posts/flowbased-vs-erlang-message-passin...