keychain persists, user defaults won't, if you store files in the documents directory it will persist if offloading the application. CoreData will NOT afaik, unless you choose to define where it persists. I'd also say that CoreData isn't exactly only meant for persisting data either - it can do that, but first and foremost it is an object graph.

more fun facts: user defaults has a limit to how big it can be. And I also think that your library would benefit from using actual types instead of Any, you can actually define this so long as the value is Codable, generics would make the library nicer to work with instead of requiring the dev to cast the type themselves. You basically just switch out Any for a generic and have the Generic conform to Codable. If targeting an iOS version that is 14+ I would just recommend using the AppStorage or SceneStorage property wrappers.