The (usually) 16 character code isn't shown by the 2FA app - it is shown by the website or service you are setting up 2FA for. It should be shown alongside the QR code, or perhaps behind a "back up" button or similar.
Never mind this, but you have just explained how this can be extracted on Aegis directly 
. I never thought it could be easily extracted like that on Aegis. But definitely 'no' on Google authenticator.This is the usual way and the best is truly to backup the secret 16 characters from the website directly. I should have commented about this along instead of only commenting on how to get it extracted through .json or .txt file while using Aegis.