But if dark matter is also interacting gravitationally, why wouldn’t it also be tangled up? And is that something we have seen in other collisions ever?
Friction between regular matter causes it to lose energy and thus velocity. Dark matter doesn't have self-interaction outside of gravity, so it just keeps going.
my first impression was this could actually be a counterexample, because there we can see the heavy, dark matter-full clusters continuing on their trajectories at full speed whereas the gas slowed down and is being left behind. compared to these 3 lightweight galaxies which seem to be alone, rather than trailing behind their dark matter-hosting parents
but perhaps these 3 _are_ going slower than their full-scale origin galaxies. I would stake my view as a layman on whether anyone can find the dark matter galaxies that spawned these farther along their expected trajectories