storybook/docs/_snippets/nextjs-app-directory-in-preview.md

export default {
  // ...
  parameters: {
    // ...
    nextjs: {
      appDirectory: true,
    },
  },
};

import { Preview } from '@storybook/react';

const preview: Preview = {
  // ...
  parameters: {
    // ...
    nextjs: {
      appDirectory: true,
    },
  },
};

export default preview;