Why is my rune that holds an array, not being reactive?

Svelte5 Web Development Question About Runes

In a separate .svelte.js file I have

export let allQuestionsRune = $state([new ObjectWithStringProperty("hi")])

Then in a button onClick method in some +page file I am doing

allQuestionsRune[0].stringProperty = "new string"

Then in a separate svelte component I am referencing this exact property as such:

<p>{allQuestionsRune[0].stringProperty}</p>

Expected behavior: I see a "hi" on the screen. Then I click the button, and I should see the "hi" change to "new string".

Actual Result: I see a "hi" on the screen. And that's it. The button is not updating at all. I thought this was supposed to be reactive ... I don't get what is going on. I have verified that the onClick method is being fired correctly.

Excerpt of some svelte documentation I don't fully understand ... If $state is used with an array or a simple object, the result is a deeply reactive state proxy. ... Perhaps this is a hint ? I don't really understand this excerpt at all.

What am I missing? Why is my rune not behaving as I expect?