TypeError: Object(...) is not a functionをどう直せばいいかわからない

Next React初心者です

*実現したいこと
next.jsでのログイン機能の実装

gitのリポジトリを真似して同じ様にログイン機能を実装しているのですが
参考リポジトリ

Server Error
TypeError: Object(...) is not a function

とターミナルのエラーが消えません
useUserファイルの
initFirebase()

が原因なのは分かるのですがどう書き換えたら良いのか分からず、
消してみたりしたのですが他のエラーが出て解決には至らず、、

ログイン機能の実装に３日もかかってしまっています。
どなたか分かる方いたらアドバイスお願いします。。

また、わからない点がありましたら遠慮なくお願いします。

useUser.js

import { useEffect, useState } from 'react'
import { useRouter } from 'next/router'
import firebase from 'firebase/app'
import 'firebase/auth'
import initFirebase from '../auth/initFirebase'
import {
  removeUserCookie,
  setUserCookie,
  getUserFromCookie,
} from './userCookies'
import { mapUserData } from './mapUserData'

initFirebase()

const useUser = () => {
  const [user, setUser] = useState()
  const router = useRouter()

  const logout = async () => {
    return firebase
      .auth()
      .signOut()
      .then(() => {
        // Sign-out successful.
        router.push('/auth')
      })
      .catch((e) => {
        console.error(e)
      })
  }

  useEffect(() => {
    // Firebase updates the id token every hour, this
    // makes sure the react state and the cookie are
    // both kept up to date
    const cancelAuthListener = firebase.auth().onIdTokenChanged((user) => {
      if (user) {
        const userData = mapUserData(user)
        setUserCookie(userData)
        setUser(userData)
      } else {
        removeUserCookie()
        setUser()
      }
    })

    const userFromCookie = getUserFromCookie()
    if (!userFromCookie) {
      router.push('/')
      return
    }
    setUser(userFromCookie)

    return () => {
      cancelAuthListener()
    }
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [])

  return { user, logout }
}

export { useUser }

FirebaseAuth.js

/* globals window */
import { useEffect, useState } from 'react'
import StyledFirebaseAuth from 'react-firebaseui/StyledFirebaseAuth'
import firebase from 'firebase/app'
import 'firebase/auth'
import initFirebase from '../utils/auth/initFirebase'
import { setUserCookie } from '../utils/auth/userCookies'
import { mapUserData } from '../utils/auth/mapUserData'

// Init the Firebase app.
initFirebase()

const firebaseAuthConfig = {
  signInFlow: 'popup',
  // Auth providers
  // https://github.com/firebase/firebaseui-web#configure-oauth-providers
  signInOptions: [
    {
      provider: firebase.auth.EmailAuthProvider.PROVIDER_ID,
      requireDisplayName: false,
    },
  ],
  signInSuccessUrl: '/',
  credentialHelper: 'none',
  callbacks: {
    signInSuccessWithAuthResult: async ({ user }, redirectUrl) => {
      const userData = mapUserData(user)
      setUserCookie(userData)
    },
  },
}

const FirebaseAuth = () => {
  // Do not SSR FirebaseUI, because it is not supported.
  // https://github.com/firebase/firebaseui-web/issues/213
  const [renderAuth, setRenderAuth] = useState(false)
  useEffect(() => {
    if (typeof window !== 'undefined') {
      setRenderAuth(true)
    }
  }, [])
  return (
    <div>
      {renderAuth ? (
        <StyledFirebaseAuth
          uiConfig={firebaseAuthConfig}
          firebaseAuth={firebase.auth()}
        />
      ) : null}
    </div>
  )
}

export default FirebaseAuth

initFirebase.js

import firebase from 'firebase/app'
import 'firebase/auth'

const config = {
  apiKey: process.env.NEXT_PUBLIC_FIREBASE_API_KEY,
  authDomain: process.env.NEXT_PUBLIC_FIREBASE_AUTH_DOMAIN,
  databaseURL: process.env.NEXT_PUBLIC_FIREBASE_DATABASE_URL,
  projectId: process.env.NEXT_PUBLIC_FIREBASE_PROJECT_ID,
  storageBucket: process.env.NEXT_PUBLIC_FIREBASE_STORAGE_BUCKET,
  messagingSenderId: process.env.NEXT_PUBLIC_FIREBASE_MESSAGING_SENDER_ID,
  appId: process.env.NEXT_PUBLIC_FIREBASE_APP_ID,
}

export default function initFirebase() {
  if (!firebase.apps.length) {
    firebase.initializeApp(config)
  }
}

検証ツールエラー
webpack-internal:///./node_modules/next/dist/client/dev/error-overlay/hot-dev-client.js:283 GET http://localhost:3000/ 500 (Internal Server Error)
Uncaught     at eval (webpack-internal:///./utils/auth/useUser.js:21:67)

initFirebaseをなくした場合,
API key not validと言われます