Many Android devices allow unlocking the bootloader and gaining root or installing an alternate OS without exploits, and there are quite a few third-party Android builds for supported devices. The process is not beyond what a person of average intelligence and modest computer skills could pull off with some patience and a video guide. Only a handful of tech nerds actually do it.
I stand by my speculation that if it were possible to do that on an iphone, it'd definitely be something loads of people would do, including a large amount of people who shouldn't open their device that way but do just because they watched someone on social media telling them to.
Wouldn't it be better to solve that with education? Also MacOS gives you a warning when you're opening something not vetted by them.
The idea that it's some higher authorities responsibility to keep us safe quickly slides into losing freedoms we care about.
Would you also like all websites to be ISP-approved?
We could also have all social media filtered through LLM guards to keep us safe?
Maybe link our IDs to our online identity to protect our kids.
I'm not arguing that anything get any more locked down than it already is, so your points (while possibly valid in a bigger discussion) don't make a lot of sense here in this discussion about a hypothetical "unlock phone" setting.