What I understand the "dark" in "dark ages" mean is that not much came out of it, in particular in terms of historical records, not that life during that time was particularly terrible.
It is dark in the "hard to see" sense, not in the "evil" sense.
Or at least, that's the idea now, it possible that the term "dark ages" acquired a new meaning over time.
“Dark” as opposed to “enlightened.” It was a dark time for knowledge and education.
I mean, IMO - that’s how I’ve always understood it.
Yes, that's the reason the early Middle Ages are called the Dark Ages (Petrarch is credited with this name), but it is simplistic.