Why My Angular 21 Upgrade Failed 👀

I believe Angular upgrades have become much smoother these days. Most of the time, a simple ng updateis enough to move to the latest version. Instead, I spent hours chasing errors that looked completely unrelated to the real problem 😭 After upgrading the project to Angular 21, I started seeing errors like these: Cannot find module '@angular/material/chips' Cannot find module '@angular/material/dialog' Then another one appeared: Error: The current version of "@angular/build" supports Angular ^19... but detected Angular version 21.x instead. At first, it looked like Angular Material wasn't installed correctly but i think the actual issue was a version mismatch inside the project. Some packages had already been upgraded to Angular 21: @angular/core @angular/common @angular/material But the build system was still using: @angular-devkit/build-angular@19 Since Angular's build tools are tightly coupled with the framework version, the compiler started pro