"Firebase Data Connect unavailable due to a known Google Cloud global outage"
While the Google Cloud status page https://status.cloud.google.com/ says "No major incidents" and everything is green. So Google Cloud know there is an outage but just deem it not major enough to show it.
Edit to add: within 10 minutes of this post Google updated their status page. More curiously the Firebase page I linked to has been edited to remove mention of Google Cloud in the status and now says "Firebase Data Connect is currently experiencing a service disruption. Please check back for status. ".