> Is it safe to assume, then, that Google and Apple already have backdoors in their operating systems as likely requested by many governments around the world

I don't know whether it is safe to assume. But if they are complying with Australian law, specifically the Assistance and Access Bill (2018) [0], then they must write an undetectable backdoor for the Australia government if asked (that's the assistance the bill's name refers to), and push it any phone the government demands (that's the access bit).

The only way to avoid this as far as I can tell is to run a free open source distribution. Unlike the paid systems such Windows and iPhone, the free distributions do not have the "billing relationship" their customers the proprietary companies are so fond of. It's that billing relationship that allows them to target only the devices owned by a specific individual.

The Australian's must do that targeting because that law demands they don't introduce a systemic weakness into every phone. Any sort of backdoor is considered a systemic weakness. I dunno what laws other countries operate under, or how well they follow the laws they do have, but I'd be surprised if Australia wasn't following its own laws. That means if your device runs a true open source distro that doesn't track it's users, in Australia its truly your device.

[0] https://www.homeaffairs.gov.au/about-us/our-portfolios/natio...