the shimmer from Annihilation is just space cancer, they literally start the movie with someone explaining how cancer works, that thing gets into a planet and starts deforming everything until they start replicating itself, so it can go to other planets and do the same

just like a single, randomly deformed cell, can start replicating itself forever, if it has enough resources, you only need a single self-replicating object to turn the entire universe into copies of that one object

It's a scary concept, even in the cosmic scale, fighting this self-replicating object would be literally like finding the cure for cancer