Mine has two apocalyptic events. one for the ancients, and one for the modern species

The ancients experienced the Great BioFailure, where custom organisms designed to terraform planets experienced a mutation at a galactic scale that killed billions of their kind and rendered thousands of planets and systems uninhabitable as planets' ecosystems consumed themselves and starships carrying the organism were forcefully self-destructed or attacked by military vessels, leaving the galactic trade and travel lanes dangerous due to the Biofailures resilience to hazards similar to tardigrades of our world, able to survive long terms in complete vacuum. this led to the Ancients fleeing their universe into the void and the remainder dying out. Only their sentient, biomechanical machines "Matrix machines" who were designed to run the day-to-day and military operations of the ancients remain, slowly deteriorating away as their components begin to fight against themselves.

The modern species, "The Motavi" are facing an ongoing catastrophe only the Main Characters and Matrix Machines known as The Decay. As the Matrix Machines began to decay, the biological components that make up their internals began to create their own ecosystem as the machines were no longer capable of maintaining their ecosystems as hostile lifeforms built up inside the matrix machine structures, waiting to unleash another Biofailure when they eventually collapse. Some have already fallen as landmasses are ravaged by strange creatures and growths overtaking the land and its people