Cloud function to export Firestore backup data. Using firebase-admin or @google-cloud/firestore?

The way you're accessing the admin client is correct as far as I can tell.

const client = new admin.firestore.v1.FirestoreAdminClient({});

However, you probably won't get any TypeScript/intellisense help beyond this point since the Firestore library does not actually define detailed typings for v1 RPCs. Notice how they are declared with any types: https://github.com/googleapis/nodejs-firestore/blob/425bf3d3f5ecab66fcecf5373e8dd03b73bb46ad/types/firestore.d.ts#L1354-L1364

Here is an implementation I'm using that allows you to do whatever operations you need to do, based on the template provided by firebase here https://firebase.google.com/docs/firestore/solutions/schedule-export

In my case I'm filtering out collections from firestore I don't want the scheduler to automatically backup

const { Firestore } = require('@google-cloud/firestore')

const firestore = new Firestore()
const client = new Firestore.v1.FirestoreAdminClient()
const bucket = 'gs://backups-user-data'

exports.scheduledFirestoreBackupUserData = async (event, context) => {
  const databaseName = client.databasePath(
    process.env.GCLOUD_PROJECT,
    '(default)'
  )

  const collectionsToExclude = ['_welcome', 'eventIds', 'analyticsData']

  const collectionsToBackup = await firestore.listCollections()
    .then(collectionRefs => {
      return collectionRefs
        .map(ref => ref.id)
        .filter(id => !collectionsToExclude.includes(id))
    })


  return client
    .exportDocuments({
      name: databaseName,
      outputUriPrefix: bucket,
      // Leave collectionIds empty to export all collections
      // or define a list of collection IDs:
      // collectionIds: ['users', 'posts']
      collectionIds: [...collectionsToBackup]
    })
    .then(responses => {
      const response = responses[0]
      console.log(`Operation Name: ${response['name']}`)
      return response
    })
    .catch(err => {
      console.error(err)
    })
}