A dark age is a low-data age. It's not dark as in a slow development age. We see the end of the Islamic Golden Age (areound the 14th-15 centuries) as as time when advancement in the Middle East slowed as astronomy and algebra were reinterpreted as sorcery against God (except when done for the religious authority or the caliphate / sultanate). Compare witchcraft and witch burnings in the late middle ages and early reniassance. Anyhow a lot of smart people got executed by the religious authority, and so development slowed, allowing Christian imperial interests from the west to catch up.

This won't be a dark age even as the US state tries to bury what happens in disinformation campaigns. There's too much archeological data to be available. Though future civilizations may not prioritize studying what happened while we navigate some great filters like the climate crisis.

It's going to suck and people will die, and some atrocities will be so heinous as to require memorials and denial movements, but it will be super hard to bury the records.

The US is going to join Russia as a has-been, but it was always a genocidal bully, and deserves to crumble like Rome.