Module '"@angular/fire/firestore"' has no exported member 'AngularFirestoreDocument'
//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