Glenn Fleishman has a good tip on how to use Apple’s two-factor authentication on older devices that don’t support it.
But 2FA and outdated versions of Apple TV, iOS, and macOS don’t mix. You try to log in on those devices with your Apple ID and popups with codes may appear on other devices, but there’s no way to enter it on the piece of equipment from which you’re trying to log in. Fortunately, there’s a simple workaround.
I always forget about the manual method.
Check It Out: Using Two-Factor Authentication on Old Apple Devices