Module @angular-fire-firestore has no exported member AngularFirestoreCollection

//Angular changed the syntax, the new import should be:
import { Firestore,
       collectionData, collection} from '@angular/fire/firestore';

//You should also change the construction:
item$: Observable<Item[]>;
  constructor(firestore: Firestore) {
    const collection = collection(firestore, 'items');
    this.item$ = collectionData(collection);
}
//Check the GitHub repo in the source for more details

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

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