How does New Zealand avoid immigration prisons?

First, after getting PR, I will stay in New Zealand for two and a half years in a row. If I have a full-time job, the time seems to be reduced. Then you can apply for a permanent visa at the immigration office. With this visa, you can go back to New Zealand at any time without sitting in an immigration prison.

Second, after completing PR, if you stay for five consecutive years (it seems to be three years), you will directly change your nationality and become a citizen. Of course, there will be no immigration supervision, but you will have to apply for a visa to China in the future.