Custom Content UX

I am trying to understand how to add a custom content type which can appear as the child of a Page in Confluence and has my own UI. Something akin to how a Whiteboard works. I have tried this:

    - key: example
      resource: main
      title: Example
      bodyType: raw
      supportedContainerTypes: [page]
      preventDuplicateTitle: true

However, this doesn’t seem to be possible? The result is akin to a type of attachment more than anything? Is this the intended use case?

There doesn’t seem to be anything on the topic at: