I have setup the Prismic Preview mode on our website and it works fine.
I have then tried using it with the "Release" feature and same, it works fine but seems limited to only display the first 20 documents included in the release. This oddly seems related to the default size of the API request to Prismic.
I have the same setup as listed in your documentation: Previews with Next.js - Documentation - Prismic (that has a minor typing error for the "preview.ts" file when using TypeScript btw).
Is there a configuration somewhere I am missing to increase the default size of 20? Or is there an issue in how the Preview component works for Releases?