I've made a verbose answer to you other question, but I believe it is as much relevant here: https://physics.stackexchange.com/a/259646/119172
From the comments on this page, I see many assumptions regarding the nature of dark matter which confuse the whole story. First, you need to understand that dark matter is a phenomenon. It is combination of matter deficiencies in many cases (e.g., see this: http://sciencewise.info/definitions/Dark_matter_by_Oleg_Ruchayskiy). Everything suggests that this is a particle (as opposed to another phenomenon, dark energy that cannot be a particle because it is constant in space), but we do not know yet it's properties.
But, since we still haven't found it, it has to hide from us very hard. This is the basic point that allows to exclude dark matter from consideration of BBN. All we need to assume is that it is long-lived and interacts mostly gravitationally. Everything else is negligible in cosmological point view.
But there's a lot of dark matter, isn't there? Yes, estimated energy content of dark matter is much more than one of the matter or radiation. But this wasn't always the case. Different kinds of matter take turns dominating the Universe because their energy fractions evolve (see, e.g., https://www.wikiwand.com/en/Friedmann_equations#/Density_parameter).
So, if dark matter is a particle, then during BBN it would either be unimportant if it is heavy (because then Universe is dominated by radiation) or will constitute yet another ultra-relativistic component of the plasma. And our cosmological measurements nowadays has a margin of error precisely for one more ultra-relativistic specie.