How to see changes to an object in a Pinia state from a component with Options API?

[pochern]

codesandbox: https://codesandbox.io/s/prod-surf-wbbmt5

Here I have a Todo List. I am trying to print a certain text in TodoList.vue depending on if any objects of the items array contain isComplete = true. The issue is that even when I check a todo item, and an item's property isComplete gets updated to true in the Pinia store, the TodoList.vue component does not see it within the computed property someTodoCompleted. The computed property does not react to that change.

How can you in a component with Options API listen to the changes of objects within an array? How to make this h2 tag display the text based on someTodoCompleted returning true?