Even if leaving the solar system, or whatever system a sentient race exists, were possible, going to war with another sentience in their home turf (which, remember, must first overcome the near impossible hurdles of getting there to begin with) is so unlikely it makes invasion fears absurd. I think the dark forest theory is groundless paranoia.
Scifi usually bypasses this by breaking the laws of physics, for the sake of storytelling.
People don't get dark forest at all.
Dark Forest isn't about hiding from invasion. It's about hiding from getting preemptively sniped by someone else, worried that one day you may find a reason and a way to snipe them.
For this to work out you don't need interstellar colonization to be plausible - merely the ability to accelerate a rock to a significant fraction of the speed of light is enough, and that's definitely much closer to science than fiction.