Lock Mode on iPhone. What is it, why and how to enable it?

Smartphone software may be vulnerable. Manufacturers release "patches" that fix problems, but this does not always happen promptly. In addition to the standard advice - monitor software and application updates, there are also additional ones - for example, do not connect to unprotected Wi-Fi networks or do not use any sources to install applications other than the official Apple and Google "stores". The iPhone has a special blocking mode for this. What is it? What restrictions does it have? How to enable it? How to manage the blocking mode?