BTW, is there an authoritative source whether these cloud backups to Google Drive are unencrypted/encrypted with Google keys, or encrypted with keys held by Facebook?
I see no reason not to encrypt them the same as local backups (with a key that is held by Facebook, and provided to your phone once they verify your phone number).
The difference between these against the US government filing warrants is just one piece of paper, but against an attacker that compromises your Google account, it does make a significant difference.
Of course you got all the metadata going to FB, but it's still a good messenger feature-wise for now, so I'll keep it as a backup in case my favorite privacy-conscious messenger is down again for 10 hours.
There is no evidence that messages ever leak outside of WhatsApp via means other than potential unencrypted backups that you may or may not be using at a cloud provider not connected to Facebook or your IME.
If you're targeted by NSO or whatever nation state that would be interested enough in you to compromise you, you got other things to worry about.
WhatsApp does filter messages on the client side but it’s stuff like submitting image hashes to the CP database. If Signal reaches the scale of WhatsApp they will be forced into doing this as well. And nothing in Signal’s architecture prevents this kind of data exfiltration the same as WhatsApp.