Duolingo Onboarding FlowSource
Uses a determinant progress bar to foster a feeling of accomplishment while communicating how much the user has progressed towards finishing the flow in a way that reduces user dropoff due to uncertainty.
The web page has minimal choices to allow the user to focus—including only onboarding-related questions with an isolated presentation.
The next step button only becomes clickable — made apparent by the color change — once the user has made a selection, providing immediate validation and nudging the user to take the only possible action.
Before asking the user to allow multiple methods of notification, the flow establishes an intention to help the user reach their goals to build trust and clearly demonstrate value.