I encountered the same problem and in the GitHub repo (https://github.com/angular/angularfire) is explained how to adjust the code for the new version

import { Firestore, collectionData, collection } from '@angular/fire/firestore';
import { Observable } from 'rxjs';
...
item$: Observable<Item[]>;
constructor(firestore: Firestore) {
    const collection = collection(firestore, 'items');
    this.item$ = collectionData(collection);
  }

You also have to change the way you initialize the app in the app.module.ts

import { provideFirebaseApp, getApp, initializeApp } from '@angular/fire/app';
import { getFirestore, provideFirestore } from '@angular/fire/firestore';

@NgModule({
  imports: [
    provideFirebaseApp(() => initializeApp({ ... })),
    provideFirestore(() => getFirestore()),
  ],
  ...
})

Angular has changed its angularfire syntax right away. Check their github repo; thus just google Angularfire github and you will see their new codes. I myself am disappointed Angular has to change their firebase codes...\