This could instead be an issue with the React docs rather than with Next, but the CodeSandbox example in the docs (you can access it directly via the "fork" link) indeed appears to be a server ...
SmartStepper is a modern, customizable React stepper component for building multi-step forms, wizards, and onboarding flows. Integrates seamlessly with react-hook-form, supports Yup/Zod validation, ...