The CAS Stories feature? It's only the initial option in a new save by design. In any other save you'll only have the option for the second Sim created in CAS (first one will pop up as it used to, when you click the Add Sim plus sign, you'll see the Storybook option). Once you have a Sim created that way, you can just delete the first one - you don't need to do anything with that Sim before starting to create the next.
Comments
it works for me now.