Indeed, maybe there was no scientific dark age in the Middle ages, at least not globally, but It was a dark age in Europe, knowledge was lost, the (roman) world economy collapsed and entirely disappeared, economic throughput and population would not recover until the industrial revolution[1]. The dark age ended when the last remaining of the ancient Roman world was forcibly dispersed from Constantinople, most of it found a safe harbor in Italian cities that would become the center of the Renaissance.[2]

[1] Ward-Perkins, Bryan. The Fall of Rome And the End of Civilization

[2] Brownworth, Lars. Lost to the West: The Forgotten Byzantine Empire That Rescued Western Civilization