Describe the problem that you experienced

Upgrading to Angular 21 introduced unexpected TypeScript and build issues due to an automatic migration of moduleResolution from "node" to "bundler" (via #64125
).

The issue is that this behavior is not clearly documented as a breaking change in the Angular upgrade guide, making it difficult to diagnose the root cause.

Enter the URL of the topic with the problem

https://angular.dev/update-guide?v=20.0-21.0&l=3

Describe what you were looking for in the documentation

I expected to find a clear mention in the Angular 21 upgrade guide that:

• moduleResolution is changed to "bundler"
• This change may introduce breaking behavior
• Guidance on how to handle issues caused by this change

Describe the actions that led you to experience the problem

No response

Describe what you want to experience that would fix the problem

No response

Add a screenshot if that helps illustrate the problem

No response

If this problem caused an exception or error, please paste it here

If the problem is browser-specific, please specify the device, OS, browser, and version

Provide any additional information here in as much as detail as you can