The ‘Dashboard Auto Refresh’ feature is only available if you use Quick Sight Capacity Pricing (see the language that says “Capacity pricing is also required for programmatic refresh of dashboards for near real-time data rendering”).
One you change your pricing model to Capacity Pricing, you can reach out to your Quick Sight account manager and they can submit the request to turn the feature on for you (it doesn’t get automatically enabled as of today). If you don’t know who your Quick Sight account manager is, you can contact quicksightsales@amazon.com.