Using 2-Factor Authentication on an older Mac
Here’s the trick: when you’re prompted for your password, type it and press Return to trigger the authentication request. Wait for the 6-digit code to appear on one of your other devices. Next, if your password isn’t still in place, rekey it, and append the code. So if your password is Pa55w0rD (it shouldn’t be—that’s way too weak!) and your code is 039602, you’d type Pa55w0rD039602 all at once in the password field.
MacBook Pro 13″, macOS 10.15