It’s quite intersting how many ways man or nature could conspire to knock 100 - 200 years of technology right out from under us. Or kill off 50% of the human race in a few years.
China suffered for about 300 years. Byzentium was down for the count for at least 80 years.
Other areas, e.g. the realm of the Arabs who looked to Mecca for economic direction, didn't notice anything had gone wrong (relative to their earlier condition). They ended up conquering pretty much the rest of remaining civilization.
There were losses beyond imagining ~ for example, Michaelangelo was the first artist in a millenum who could produce sculpture the equal of the best produced by sculptors in Classical Times.
That's how much knowledge of that particular technology (sculpting) that had been lost.