When I log into my Google account from my laptop with 2FA enabled, I usually get a prompt on my smartphone in order to confirm the log in. I tap OK and then I am logged in.
However sometimes I am not immediately logged in after that. My laptop then shows a screen like this:
Then on my smartphone I get something like this:
(It is not always laptop+smartphone. Actually in this particular case I was logging in to Google in a webbrowser from my smartphone, so everything happened on a single device).
I wonder what Google is trying to achieve with choosing a number. What type of attack would be averted by this?
I tried to Google something about that, but I found nearly nothing at all. (One not-helpful twitter post is what I found)