Bootstrapped components are defined in the bootstrap property of an @NgModule decorator or as the first parameter of bootstrapApplication for standalone components.
This error happens when Angular tries to bootstrap one of these components but cannot find its corresponding node in the DOM.
Debugging the error
This issue occurs when the selector mismatches the tag
@Component({ selector: 'my-app', ...})class AppComponent {}
<html> <app-root></app-root> <!-- Doesn't match the selector --></html>
Replace the tag with the correct one:
<html> <my-app></my-app> <!-- OK --></html>