I was looking at a companies that to do repairs to iPhones to decide if I wanted to DIY or just pay someone to do it, and noticed one company that listed a service named "Remove Passcode". This was concerning to me since I assumed that the iOS passcode was secure; meaning for example that it was part of the boot/build, and without it correctly presented, the phone's data was not accessible. (Yes, I know, silly to think that would be the case.)
Anyway, at this point after quickly researching the topic, it appears it's possible to delete one file, turn the phone on, have complete access to it, replace the file, and no one would be the wiser.
Not asking for a how-to – just confirmation that the passcode is meaningless security-wise.
Best Answer
One a malicious individual has physical access to the hardware, any protection becomes meaningless, security-wise.
If an attacker had the time and resources, they could circumvent any UI-based security by removing (de-soldering) the flash from the logic board, connecting it to another system, and reading any data off them. Only full-disk encryption would block that, but, given physical access and/or time, that's defeatable, too.