Lockdown Mode

“Lockdown mode is a dramatic change to how the iPhone works, so it's not something that's meant for everyone. It's meant for people who might be at greater risk of being targeted by hackers with spyware, like journalists and other public figures. So you probably shouldn't enable it on your devices, but it's an example of Apple doing what it can to protect people who need the highest level of security possible on their iPhone and other Apple devices.”