There is a large amount of $$$ that goes into security of iOS and iPhone (sometimes orthogonal to privacy, sometimes not) that does not go into a dumbphone. The iPhone is also much more scrutinized and researched into than a random dumbphone, so it is plausible that you get much more exposure to exploits, etc., using a dumbphone that does not get updates etc.
It seems unlikely they put the same efforts into finding a zero day for a nokia. There might be a super easy to find zero-day though, like you're saying.
If it's anything like the old days, they don't need to horde a 0 day.
There were always obscure pieces of software that would pull your forgotten pin right off the device with the right secret code, in which case you have full access to the device.
I'd also expect them to be vulnerable to much simpler attacks like just reading flash chips directly
> On the other hand, China is known to have and use ios zero days
What's your threat-model? If your adversary is a nation-state on par with China, you're probably toast unless you have a well-resourced entity supporting you (think large corporate or another nation-state)
But the majority of that security is required due to the vulnerabilities that come with the smart part of smartphones. A dumb phone has a much smaller attack surface. If I use the phone solely for texting and the occasional tethering and phone call, my exposure is automatically seriously reduced.
The dumb phone has no access to the pocket computer, after all.
There is a large amount of $$$ that goes into security of iOS and iPhone (sometimes orthogonal to privacy, sometimes not) that does not go into a dumbphone. The iPhone is also much more scrutinized and researched into than a random dumbphone, so it is plausible that you get much more exposure to exploits, etc., using a dumbphone that does not get updates etc.