Melissa Scott’s 2023 Fallen is the second book in her Firstborn, Lastborn space opera series. It shares no characters with the first book, Finders, and is set in a different period. More on that second detail later.
The invention of nigh-godlike AIs provided the Ancestors with everything they could have wanted… until they found themselves at war with the AIs. Civilization collapsed. Centuries later, civilization has recovered, although at a lower tech level than the Ancestors enjoyed.
Luckily for the revived civilization, space is littered with Ancestor relics. A few of these relics aren’t existential threats.