I reworded the title of the topic because it was too long.
If you think that I misunderstood the issue then please provide a concise title.
Now regarding the question I think that it would be best if you could provide a sample repo that showcases what you’re trying to do. As in the exact structure of the Page Bundle with its headless bundle (snippets) and the relevant shortcode.
Again, it would be best to publish a repo. You haven’t provided the contents of layouts/shortcodes/example.html. As far as I know, shortcodes are meant to be used in regular content files and not included through layouts.