Some classic (and much-loved) Netlify features were born when most sites we hosted were fully static. For example, Netlify Forms do their magic based on automatic detection of specially-marked form tags in static HTML files.
This has required some adjustments for the age of SPA and SSR. With modern Next.js versions, no page is truly static: as a developer, you can revalidate any page. However, you can still use our forms.
Below is a simple form using fetch to submit its data to Netlify rather than using full-page navigation. To be detected, form tags must be hosted in static files -
and public/__forms.html exists just for this purpose.
Deploy this site to your Netlify account, enable the forms feature in the UI, trigger a build and you can start collecting submissions.