Hi Michael,

Starting with Angular v21, zoneless change detection is enabled by default. Since Kendo components still do not provide support for zoneless, it is expected to face some issues, especially for operations that require change detection.

To keep the Kendo components functioning as expected, it's crucial to add the provideZoneChangeDetection({ eventCoalescing: true }) in the main.ts file providers:

main.ts:

import { provideBrowserGlobalErrorListeners, provideZoneChangeDetection } from '@angular/core';
import { bootstrapApplication } from '@angular/platform-browser';
import { provideAnimations } from '@angular/platform-browser/animations';
import { App } from './app/app';

bootstrapApplication(App, {
  providers: [
    provideBrowserGlobalErrorListeners(),
    provideAnimations(),
    provideZoneChangeDetection({ eventCoalescing: true }),
  ],
}).catch((err) => console.error(err));

zone.js still needs to be provided in the polyfills array of the angular.json file.

You mentioned that Zone is being used, but based on the provided details so far, I am not sure how Zone.js is actually being enabled for an Angular 21 application. 

Please follow the suggestions above and let us know how it goes after using provideZoneChangeDetection in main.ts.

Regards,
Martin Bechev
Progress Telerik

Hi Michael,

Thank you for the prepared demo.

The zoneless change detection is enabled by default from Angular v21. Since Kendo Angular components still do not provide full support for it, the developer needs to:

1. Install the zone.js package and then import it in the angular.json polyfills array.

2. Provide provideZoneChangeDetection({ eventCoalescing: true }) in the app.config.ts file (or directly in main.ts).

The steps can also be found in this article:

https://www.telerik.com/kendo-angular-ui/components/knowledge-base/cannot-read-properties-of-undefined-grid

We are currently actively working on providing support for zoneless, but at this point we cannot commit to an exact date when this will be available for the TreeView.
Some smaller components already have the proper configuration to support zoneless, but bigger ones require some more time to refactor and adjust the code. Until full zoneless support is provided, please use the approach suggested above.

Here is the updated demo:

https://codesandbox.io/p/sandbox/kendo-angular-treeview-cd-problem-forked-kx5s2k

Do let us know how it goes.

Regards,
Martin Bechev
Progress Telerik