Are there inaccuracies around the portrayal of why and how the reactor failed?

I don’t think there are fundamental inaccuracies about that, but there are many exaggerations about the immediate aftermath. E.g. the fireman’s hand burning from touching a graphite fragment stood out as a particularly egregious one. And it is in fact shown that the disaster was caused by incompetence and carelessness, which does support GGPs point.