Parallel routes are rendered unnecessarily

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
      Platform: darwin
      Arch: arm64
      Version: Darwin Kernel Version 22.5.0: Thu Jun  8 22:22:20 PDT 2023; root:xnu-8796.121.3~7/RELEASE_ARM64_T6000
    Binaries:
      Node: 18.16.0
      npm: 9.8.1
      Yarn: 1.22.19
      pnpm: 8.6.10
    Relevant Packages:
      next: 13.4.13-canary.5
      eslint-config-next: 13.4.12
      react: 18.2.0
      react-dom: 18.2.0
      typescript: 5.1.6
    Next.js Config:
      output: N/A

Which area(s) of Next.js are affected? (leave empty if unsure)

Routing (next/router, next/navigation, next/link)

Link to the code that reproduces this issue or a replay of the bug

https://github.com/slvstr-dev/test-parallel

To Reproduce

• Install project
• Run project locally
• Check console for logs of both routes

Describe the Bug

In layout.tsx I want to render conditionally render a parallel route, f.e. if a user is logged in or not. Currently it runs code from both routes. Console.log's of both page.tsx in root and page.tsx in @auth are being run.

Expected Behavior

Based on the condition I only expect the console.log from the returned page to run.

Which browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

Start with the linked reproduction project and inspect its layout.tsx, root page.tsx, and @auth/page.tsx files. Run the project locally and compare the console output from both parallel routes with the condition in the layout. Done means only the conditionally returned route executes.