True, though the device could simply not be connected to that chat if the user doesn't want to implement the policies necessary to access that chat.

The major hole here is that you turn off your notifications and don't have a bunch of database records, but the threat actor somehow finds out who your contacts are, gets a hold of their phone, and can then see all of the messages you sent via their notifications database. So if you want to trust the device for secure communications, you can't do that.