Algolia
We use algolia for full text search as Firebase does not support this natively. Below is the Firebase guide showing how to enable full text search and the full algolia docs:
Full-text search | Firebase
Most apps allow users to search app content. For example, you may want to search for posts containing a certain word or notes you've written about a specific topic. Cloud Firestore doesn't support native indexing or search for text fields in documents. Additionally, downloading an entire collection to search for fields client-side isn't practical.
https://firebase.google.com/docs/firestore/solutions/search
Algolia Docs
Algolia: across 15 languages, read up on Algolia concepts, get access to tutorials with concrete use-cases and sample datasets, or explore our API Reference.
https://www.algolia.com/doc/