The Core Web Vitals of your Next.js application could be tracked and sent to any backend of your choice.

Earlier version of Next.js enable tracking by specifying analyticsId into your next.config.js file.

This configuration mechanism will be removed in nextjs@15, as it could be elegantly replaced with useReportWebVitals built-in hook.

To remove this warning, you must remove analyticsId from your next.config.js file.

To keep tracking your Core Web Vitals, you could:

• use useReportWebVitals hook as explained here and send the metrics to any backend of your choice.
• install and use @vercel/speed-insights package into your application