Sidebar not rendering in Nextra v4 with Next.js 15.4.6

[itsalimanuel]

Versions

"next": "15.4.6",
"nextra": "^4.2.16",
"nextra-theme-docs": "^4.2.16",
"react": "19.1.0",
"react-dom": "19.1.0"

Reproduction steps

1. Install Nextra 4 in a Next.js 15 app.

2. Project structure:

   app/docs/
   ├── layout.tsx
   ├── _meta.json
   ├── page.mdx
   ├── about/page.mdx
   └── frameworks/page.mdx
   

3. app/docs/layout.tsx:

   import { Layout } from "nextra-theme-docs";
   import { getPageMap } from "nextra/page-map";
   import "nextra-theme-docs/style.css";
   
   export default async function DocsLayout({ children }: { children: React.ReactNode }) {
     const pageMap = await getPageMap();
     console.log("PAGE MAP:", pageMap);
   
     return (
      <Layout
      navigation={true}
      navbar={navbar}
      search={search}
      sidebar={{ defaultOpen: true }}
      pageMap={await getPageMap()}
      docsRepositoryBase="https://github.com/shuding/nextra/tree/main/docs"
      footer={footer}
    >
      {children}
    </Layout>
     );
   }

4. _meta.json:

   {
     "index": "Home",
     "about": "About",
     "frameworks": "Frameworks"
   }

5. Run bun run dev → open /docs.

Expected behavior

• A sidebar should appear on the left, listing Home, About, and Frameworks.

Actual behavior

• No sidebar is shown.
• Only the main content (page.mdx) renders.

Notes

• Tried both _meta.json and _meta.js.
• Cleared .next/ cache and restarted.
• Behavior persists with a minimal layout.tsx and no custom overrides.
• Possibly related to navigation / _meta.json not being picked up in App Router mode on Next.js 15.

[JimmyAppelt]

I can confirm same 🙂 #4725 (comment)

Related issue #4725

[dimaMachina]

Updating next to ^15.5 fix this issue (tested 15.5.0, 15.5.3 and latest canary 15.6.0-canary.20)

ref #4725 (comment)