For Marxists, the state is the institution that tries to resolve, with violence, the contradictions that are inherent within class society. So when class society no longer exists, then violence is no longer necessary, hence the state is no longer necessary, hence “withering away”.

This isn’t an all or nothing situation, just a theory. The laws of uneven and combined development indicate that this withering would happen in different ways at different rates. this process wouldn’t even begin until the whole world has become some form of socialism, and the social relations governing society would be much progressed. Its hard to imagine how this would work compared to our current situation