Fetching all collections in Firestore

There are limited public APIs to get a list of top-level collections. Mobile clients (Android, iOS, web) have no API. Node.js admin clients have listCollections() on Firestore to get that list. Or, if you're looking for subcollections nested under a document, use DocumentReference.listCollections().

If you want to get a list on any platform, you should maintain that list yourself in a known collection inside a known document id.

You can do the following:

const admin = require("firebase-admin");
const db = admin.firestore();

db.listCollections()
  .then(snapshot=>{
      snapshot.forEach(snaps => {
        console.log(snaps["_queryOptions"].collectionId); // LIST OF ALL COLLECTIONS
      })
  })
  .catch(error => console.error(error));

This works with NodeJS.
Remember that you will need to download firebase-admin and do the necessary configuration for Firebase server side.

You can make a separate collection(say listOfCollections) which contains all the other collection names as documents or in an array of strings in one document as an alternative.

Then, whenever you are adding a new collection first add its name to the listOfCollections.