Can you add to Instagram highlights without adding to story?
You need to go to Instagram Settings > Story Controls > Hide story from. Deselect Everyone. That’s how you can add Stories to Highlights without anyone seeing them.
Why can’t I add to highlights on Instagram?
For proper functioning of Instagram highlights, a setting known as Save to archive should be enabled. That saves your stories in your archive. Later, you can add any past story to your highlight. If that isn’t enabled, you will not be able to use Instagram highlights.