Export firebase real-time database collection to Bigquery

There is no built-in or pre-built extension that I know of to provide a similar export to BigQuery from the Firebase Realtime Database. It sounds like a reasonable feature request though, so I recommend filing it here.

In the meantime, keep in mind that all Firebase Extensions are open-source, so you can take the code for the firestore-bigquery-export extension and use that to either create your own extension for RTDB, or otherwise set up an export.