Sandbox Signing in doesn't work on iOS 14

I created a sandbox user in appstore connect then tried to sign in in the iPhone settings going to App Store > Sign In (sandbox account).
Apple ask for TFA, then dismiss and that's it. It never log in or show some kind of error.

I tried doing it from my app as well but the app show me a sandbox alert saying that I should setup in iPhone settings.

This didn't happen when I was testing on iOS 13.