Austria have passed a law instituting an unvaccinated lockdown
Princess, but that's a very different thing to being able to enforce it.
I don't know enough about them and the way their society is organised to ascertain whether it's actually going to work there, but I'll tell you why it won't here. We don't have the police numbers or intelligence to be able to stop millions of people from private socialising. That didn't happen during lockdown, when it was at least visibly illegal, so it certainly isn't going to when the only way to identify whether a person is breaking the law is to have up to date access to their medical records.
There are unvaccinated people living with vaccinated people, and you'd never be able to prove who was the one being visited. For mass events, it's already been explained that the security to ensure people are genuinely using proof of their own vaccination not someone else's isn't going to exist in a lot of places. It would be too impractical and expensive, so you'll get lip service instead. And as you don't need ID to get vaccinated, and that won't be introduced because it would serve as a deterrent, if there were actually any possibility of an unvaccinated lockdown with any real teeth, people would start paying others to go and get vaccinated in their name.
This sort of thing is just not viable in a society where there are no ID cards and not enough police to enforce it. And that's really very obvious if you stop to think at all about the practicalities.