two factor / 2-factor authentication field missing on App Store and disable option missing under 'manage my ID'

I have the same problem

On some devices, there is no second field; you have to add the 6-digit code to the end of your password. So if your password is ManyHorses and your code is 123456 then you enter:

ManyHorses123456

A helpful FAQ is here.

I'm gonna say 2 things:

1. Wow...
2. LOL

So that works, great thanks! Now, may I ask how did you find out about this?

Today I spent nearly an hour with Apple's Dev Tech Support and they never mentioned this and were even trying to pull the "well we don't support beta software so if your AppleID is not good for the AppStore is your fault." :/ And I kept telling them this is not about beta software, it's about them having signed me up for a beta version of the concept of the Apple ID basically, which is affecting my vanilla environment (i.e. I could no longer donwload updates for the offical XCode from the appstore, because there was no 2nd field) since the AppleID is one and only.

One thing I'll add to the answer, just in case: I tried this for the AppStore without a space in between my pwd and the second code; the answer shows a space between both, but it might work that way too.

I saw Two-Factor Authentication advertised as a new feature so I put it into the search bar of the Developer site and it led me to the FAQ.

I'm told it works both with the space and without, but the FAQ doesn't mention the space so I'll remove it in my answer above.

This does not work for me, the verification code is sent to my El Cap Mac only AFTER I click the sign in button which is useless.