It looks like you are using the Firebase SDK 8 code but probably has installed the Firebase SDK 9 version. Your code should look like this with the new SDK:

import { getFirestore } from "firebase/firestore";
import { initializeApp } from "firebase/app";
import { getAuth} from "firebase/auth";

const firebaseConfig = {
  apiKey: "x",
  authDomain: "x",
  projectId: "x",
  storageBucket: "x",
  messagingSenderId: "x",
  appId: "x",
};


const app = initializeApp(firebaseConfig);
const db = getFirestore();
const auth = getAuth();
export { db, auth };

Here you can find more about the migration to the SDK 9 version.

Here is an example how to use the new SDK 9 with collections:

import { collection, onSnapshot } from "firebase/firestore";

const unsubscribe = onSnapshot(collection(db, "cities"), () => {
  // Respond to data
  // ...
});

// Later ...

// Stop listening to changes
unsubscribe();