Space

Yeah, if you’re going dark forest and AI, you could do a lot with even a K1 civilization, which makes a Dyson swarm kind of silly, anyway. Unless you put the effort into it, in which case it would be difficult to effectively fight a K2 civilization, especially a multi-system one, because the power, numbers, and capability to spread make options other than hiding not make much sense, anyway.

I'd argue that the Dyson sphere is a method of hiding your whole solar system if done right - you put out your torch, which reduces the likelihood of visual detection, while also being able to safely expand your civilization throughout your solar system. Von Neumann probes would probably be a terrible idea in a dark forest scenario, since their communication should come back to you, spreading your position far and wide.

The Bobiverse gives some ideas about what some good probes can do, and the Culture gives some ideas of just the kind of power an advanced civilization can have. Darwin’s Radio has some good ideas about the dark forest and interstellar wars/genocide, and some interesting ideas about the nature of reality and matter itself.

Thanks for the recommendations!