You can still sign up, but it's a bit of a pain. When you initially enable 2FA, you won't be given the option. But you can register with SMS/U2F/etc. Once you'

You can still sign up, but it's a bit of a pain. When you initially enable 2FA, you won't be given the option. But you can register with SMS/U2F/etc. Once you've enabled the first authentication method, you can go into your 2FA settings and add a virtual 2FA device. Once that's done, you can go back and delete whatever you added initially to be left with only a virtual 2FA device.