verifyIdToken method doesn't exist in Auth type using getAuth from firebase/auth

I'm trying to follow the example given here where it shows the following example to verify an ID token:

// idToken comes from the client app
getAuth()
  .verifyIdToken(idToken)
  .then((decodedToken) => {
    const uid = decodedToken.uid;
    // ...
  })
  .catch((error) => {
    // Handle error
  });

My code looks like this:

function createFirebaseAdminApp(config: AppOptions) {
    if (getApps().length === 0) {
        return initializeApp(config);
    } else {
        return getApp();
    }
}

const options: AppOptions  = {
    credential: cert({
        projectId: process.env.FIREBASE_PROJECT_ID,
        clientEmail: process.env.FIREBASE_CLIENT_EMAIL,
        privateKey:
            process.env.FIREBASE_PRIVATE_KEY != undefined
                ? process.env.FIREBASE_PRIVATE_KEY.replace(/\\n/g, "\n")
                : "",
    }),
    databaseURL: process.env.FIREBASE_DATABASE_URL,
};


const firebaseAdmin = createFirebaseAdminApp(options) as FirebaseApp;
const adminAuth = getAuth(firebaseAdmin);
adminAuth
    .verifyIdToken(token)
    .then((decodedToken) => {
        res.locals.decodedToken = decodedToken;
        next();
    })
            .catch(() => {
                next(new HttpError("Invalid token provided", 403));
            });

But I keep getting

Property 'verifyIdToken' does not exist on type 'Auth'

I have the latest version of the firebase package, which I assume the example given by the docs is using considering it uses getAuth, so can't tell what I'm doing wrong. Also I'm trying to avoid mixing firebase-admin and firebase, not sure if this is correct, but if I mixed them I can't seem to avoid having to initialize too App instances.

Thanks for any help!