Consider the following when choosing between database modes:
Use Cloud Firestore in Datastore mode for new server projects.
Cloud Firestore in Datastore mode allows you to use established Cloud Datastore server architectures while removing fundamental Cloud Datastore limitations. Datastore mode can automatically scale to millions of writes per second.
Use Cloud Firestore in Native mode for new mobile and web apps.
Cloud Firestore offers mobile and web client libraries with real-time and offline features. Native mode can automatically scale to millions of concurrent clients.