NG8001: 'firebase-ui' is not a known element:

I earlier had a project with firebaseui 4.2.0 and recently created a new project which has firebase ui 6.0.2. My older project code looks like below:

 <ng-container *ngIf="core.loggedIn == false">
        <firebase-ui
        (signInSuccessWithAuthResult)="successCallback($event)"
                 (signInFailure)="errorCallback($event)">
        </firebase-ui> 

login.component.ts

export class LoginComponent implements OnInit {

  constructor(public core:CoreService,
    private afAuth: AngularFireAuth) { }

  successCallback(data: FirebaseUISignInSuccessWithAuthResult) {
    console.log('successCallback', data);
    this.core.loggedIn = true
  }

  errorCallback(data: FirebaseUISignInFailure) {
    alert('Failed to login')
    this.core.loggedIn = false
    console.warn('errorCallback', data);
  }

  

  ngOnInit() {
    this.afAuth.authState.subscribe(d => {
      //console.log('subscribed to firebase auth' + JSON.stringify(d))
      if(d == null){
        this.core.loggedIn = false
      }else{
        this.core.loggedIn = true
        this.core.email = d.email!
        console.log("user logged in fetch user role for:" + d.email)
        this.core.openMenu('admin')
      }
    });
  }

}

Now in the new project I am getting the following error

src/app/login/login.component.html:3:9 - error NG8001: 'firebase-ui' is not a known element:
1. If 'firebase-ui' is an Angular component, then verify that it is part of this module.
2. If 'firebase-ui' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

3         <firebase-ui
          ~~~~~~~~~~~~
4         (signInSuccessWithAuthResult)="successCallback($event)"
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
5                  (signInFailure)="errorCallback($event)">
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  src/app/login/login.component.ts:17:16
    17   templateUrl: './login.component.html',
                      ~~~~~~~~~~~~~~~~~~~~~~~~
    Error occurs in the template of component LoginComponent.

Has things changed since 4.2.0? Please advise how to fix it

There are several reasons for error NG8001 and from the attached snippets it is hard to tell where is the problem.

Have you added firebase-ui to your selector?

@Component({
  selector: 'firebase-ui',
  // ...
})

Also, you can check RaphaelJenni GitHub repository and compare your code to that implementation.