I'm confident there is some sort of capability for Aus intelligence agencies, and five eyes by definition, to intercept WhatsApp and Signal messages.
How that may work is a bigger question. I suspect indirect. For example: silent and targeted deployment of a "software update" to a specific ios or Android device.
Companies break state surveillance capabilities all the time. With every patch some opportunities close which is why agencies hoard exploits to give them a resilient capability. Apple doesn't take permission, we know this from their pushback against the FBI trying to get them to change code to unlock that iPhone.
