how much do humans fall back technologically?

After civilizational collapses like the Fall of Rome or the Bronze Age Collapse, how much do humans fall back technologically? After civilizational collapses like the Fall of Rome or the Bronze Age Collapse,

Europe forgot how to construct sewers for nearly 1500 years, but toilets were still used (by some… look kids! This one is self cleaning)

Weapon and metal manufacturing technology only hiccuped before improving very quickly.

Ability to work in stone took about a thousand years to relearn to the same scale. St Paul's cathedral dome (London) was a work as great or greater than any western Roman building (and it may even have been bigger than the dome in Constantinople). That was 17th century.

Arch technology was remembered and improved by 1300 with the gothic arch (better weight distribution). This allowed taller buildings with less internal supports, which are also narrower

Ability to manage water was remembered at a basic level, but only with the canal building programmes were Roman water movement surpassed.

Government systems stagnated for a while (you can choose dictator or benevolent dictator?) Until the birth of Democracy (no point listing the other two failed systems). Democracy built on the legacy of Greece and Rome, but as an ideal more than how they actually worked.

Agrarian technology started improving in the middle ages with the concept of crop rotation. The invention of the horse collar in the 12th century freed people from slavery (Europe, yes I know they had it in China 1500 years before but this is an example of parallel development not technology transfer). Now a horse could do the work of nine men but consume the food of three (Hey you! Useless peasant slave, you're free! Get lost, you've been replaced).