There are a lot of problems with the dark forest hypothesis, the most critical for this purpose being that it is not a stable outcome. A civilization with the capability to create a Dyson sphere and harness the power of an entire star could easily defeat any invader attracted to their presence. E.g. with gamma-ray lasers that fry anything and everything that might be hostile.

Even with the most advanced technology we can imagine, you can't expect to be able to detect a neighboring civilization, cross the gap between stars with an invading fleet, and arrive with enough power to overwhelm defenses every single time. Local development of solar system resources is inherently an exponential process, whereas mustering of interstellar resources is quadratic. A potential dark forest / wolf entity (I much prefer Alastair Reynolds over Liu Cixin) would have to arrive right within the (cosmically brief) window of opportunity in which a developing civilization announces its presence but before it achieves Type II status on the Kardashev scale. Statistically, someone will eventually be lucky enough to avoid the wolves long enough to get that far, and then they'd have the capability to defend themselves from any plausible enemy.

Where are the Dyson spheres of those civilizations?