Here it is, straight from the horse's mouth. You may not like it, but just the facts, ma'am, just the facts. :)
Can I turn off two-factor authentication after I’ve turned it on?
If you already use two-factor authentication, you can no longer turn it
off. Certain features in the latest versions of iOS and macOS require
this extra level of security, which is designed to protect your
information. If you recently updated your account, you can unenroll for
two weeks. Just open your enrollment confirmation email and click the
link to return to your previous security settings. Keep in mind, this
makes your account less secure and means that you can't use features
that require higher security.
Is this different than Apple’s current two-step verification feature?
Yes.
Two-factor authentication is built directly into iOS, macOS, tvOS,
watchOS, and Apple’s web sites. It uses different methods to trust
devices and deliver verification codes, and offers a more streamlined
user experience. You need two-factor authentication to use certain
features that require improved security.
The older two-step verification feature continues to work separately for users who are already enrolled.