What does hidden challenge mean?
If you are creating a challenge and would like to keep it as a Hidden, you can click on Advanced Settings and toggle on "Secret challenge" (Hide from activity feed). When you toggle this on, your challenge will not show up in anyone's Newsfeed, the Explore page, and all notifications are hidden.
To make a challenge Hidden that you have already created but has NOT started, you can Swipe up on the bottom drawer inside the challenge and click on More > Edit Challenge > Advanced Settings > Toggle on "Secret challenge".
You cannot make a challenge hidden after you have already started a challenge. Please reach out to firstname.lastname@example.org for any issues or questions.