Can the Apple ID be sign out on its own? Or dose it have to be done manually

If there is a problem with the account (such as Apple’s automated systems detecting fraud on it or someone trying to hack it) your Apple ID can be signed out automatically. Also, there are several places where you need to enter your password even if you are already signed in, such as changing your payment methods or changing your password. But other than these you need to sign out intentionally.

Proof of what? For one thing, if Find My is activated on the phone it can’t be signed out without the password, because that would defeat Activation Lock. The only thing that can be signed out remotely is the iTunes & App Store. I should have said that earlier.

A hacker who knows the Apple ID and password can put the phone in lost mode and erase it, then remove it from the account. But Apple will never do that.