No, they're not just trying to find an equation, which may not be possible. They say it's impossible to predict where the objects will be in the near term, which is nonsense.

The three-body problem doesn't say it's unpredictable, just that there is no universal equation to describe it. You can still determine where things will be with a high degree of probability with iteration. The earth, sun, and moon are a three-body problem but we know where they will be tomorrow, next year, next century, next millennium, etc. The error bars increase with time but the moon isn't suddenly going to be ejected beyond the orbit of Pluto in an unpredictable way due to some bullshit from the chaos of the three-body problem. The entire solar system is a (very large number)-body problem, but we know where every major body is going to be with a large degree of certainty for a long time.

Whether or not they could have found a way to preserve their civilisation thorough the periods inimical to life is also beside the point. They claim they couldn't predict the occurrences, which is bullshit. You don't need a computer for that, even a biological computer (which I admit was actually kind of a cool concept), you just need paper and pen.

You can't have pretentions to hard sci-fi and just talk nonsense. Either be hand-wavy soft sci-fi or make your explanations conform to our best current understanding. You can't try to explain shit and also get the most basic concepts wrong.