They do use handheld and never define it, but I can hold my laptop with my hand so I'm not sure that's necessarily a good way of disqualifying laptops. That also seems to strictly apply to the operating system ("runs an operating system designed [...] for software applications on handheld electronic devices"), which might be a fun legal quagmire as well since Linux is designed for all sorts of platforms. If I install Linux on my (formerly) Windows laptop does it suddenly become a mobile device?
It does bring up another interesting niche of computers: handheld PCs, especially handheld gaming PCs. Does this law apply to Steam Decks?
This whole thing screams "written by tech illiterates" since it seems to ignore regular computers and only focus on phones when it's all just variations of the same thing -- form factor and the software running on top isn't very relevant to whatever goal I presume they're trying to achieve. If they really want to collect everyone's ID, age, and other privacy-violating information they'd be better off doing it everywhere. But maybe I shouldn't give out advice for speed running fascism...
The author's take is a bit baffling to me. Trying to apply the US constitutional amendments against a foreign government institution to protect a US company is dumb. Those amendments strictly apply to the US government. As long as the company provides services in the UK, they are subject to UK laws on those services. If I start shipping firearms from the US to the UK it'd be perfectly reasonable for the UK to stop those packages at the border and destroy them. Network packets don't just magically transcend borders.
The reasonable consequence of noncompliance is to block the service. Yes, that's essentially paving the way for a national internet filter like China's Great Firewall, but that's why we have to fight the entire law not just the enforcement of it.
The Online Safety Act is horrible and a nightmare for so many reasons, but arguing it's unenforceable on the grounds of being in a different country is just blatantly wrong.