Correct. Only users without 2fa were in danger.

In general, yes, this is possible. However, it is more difficult than just disabling IPv4 on all your devices.

First of all, there are still many (more or less relevant) sites that still are IPv4-only. If you want to reach them via your IPv6-only home network, you need to set up or use services that translate your traffic from IPv4 to IPv6 and vice versa. But this can be error-prone and needs work and understanding of the matter from your side.

The easiest is that you just leave IPv4 and IPv6 enabled in parallel. Your operating system will usually prefer IPv6 over IPv4 if it’s available.