I've written a post about implementing a next.js front-end for Umbraco using the #ContentDeliveryApi . There's a lot of next.js specific stuff in there, but anyone working with the content delivery API should find it useful
step-by-step implementation guide: https://www.etive-mor.com/blog/a-nextjs-frontend-for-your-umbraco-site
Static demo site: https://etive-mor.github.io/umbraco-nextjs-demo/