The privacy labels are larger buckets than what I went into, and they err on the side of being more inclusive. For example, Firebase collects usage data on notifications (when they are received, opened, etc.) by virtue of being used, so that privacy label cannot be removed. It's possible some of the "diagnostics" can be taken off the privacy label.
Is it possible to entirely disable FCM in the client to avoid its phoning home to Google? If I wanted Google to have my home event data I would just use Google Home.
Yes. The toggle in Privacy will make the app not initialize Firebase. The library will still be in memory, but I don't believe it does anything. I also do not want Google to receive anything, which is why it's going to be removed once we have a replacement.