Open a to-do, tap Repeat, and “Make it a habit” now has an automated test walking the exact path a finger takes — so this button can't quietly stop working in a future change.
If it ever felt unresponsive, an out-of-date copy of the app was usually the cause. This update refreshes cleanly; tap “Update ready” when you see it.
One note that hasn't changed: a to-do carrying a checklist or a screenshot can't become a habit yet, and it will tell you so rather than looking like nothing happened.