Angular: canactivate auth gaurd issue

I am learning angular 13 & i am stuck at point, below is the code

this is my authservice file

export class AuthService {
  loggedIn = false;

  isAuthenticated() {
    const promise = new Promise(
      (resolve, reject) => {
        setTimeout(() => {
          resolve(this.loggedIn);
        }, 800);
      }
    );
    return promise;
  }
}

i am getting this error

this is my auth guard service file

import { Injectable } from '@angular/core';
import {
  ActivatedRouteSnapshot,
  CanActivate,
  Router,
  RouterStateSnapshot,
} from '@angular/router';
import { Observable } from 'rxjs';
import { AuthService } from './auth.service';

@Injectable()
export class AuthGuardService implements CanActivate {
  constructor(private authService: AuthService, private router: Router) {}

  canActivate(route: ActivatedRouteSnapshot,
    state: RouterStateSnapshot): Observable<boolean> | Promise<boolean> | boolean {
    return this.authService.isAuthenticated()
      .then(
        (authenticated: boolean) => {
          if (authenticated) {
            return true;
          } else {
            this.router.navigate(['/']);
          }
        }
      );
    }
}

screenshot of error

Can anybody help me??