You can make the expert mode dialog say "Clicking this button will erase your hard drive, drain your bank account, and give your dog cancer" and people will still click it.
Me: ...
For example, you can be the administrator on Grandma's device and block access to third-party app stores which cannot be overridden by anyone (including the device manufacturer) without your credentials. Alternatively, you could delegate that authority to a provider you trust. No one is saying you can't keep choosing Apple's walled-garden app store as the only store provider or that you shouldn't be able to block any or even all app stores. Options like that can even be locked by one-time hardware fuses so they can never be changed - even by the owner. The only issue here is Apple forcing a sole monopoly on that control for themselves because it's worth billions of dollars - instead of device owners having a choice.
Err.. Isn’t that exactly what the EU is saying?
And I love how the response to shit mobile security is to lock down devices so the people who buy them don't actually own them. Instead of, y'know, actually cleaning up the security posture of these devices.
And to provide a counterpoint, my dad can barely navigate his iPhone. I literally spent an hour on the phone with him when he was lost and needed directions; it took 20 minutes to guide him to open the messages app so he could read the address I sent. Someone that clueless isn't searching the internet to figure out workarounds for installing anything.
...they reap the consequences of their actions.
A warning lets a person know it is getting deeper. It is up to the person to realise if they are out of their depth.
If a person lacks the self reflection to realise their capabilities then they need a guardian. Children and the elderly routinely have this for other aspects of life. Why not a phone?
Why can't I delegate such authority to others when I become old and infirm?