How accurate are NK statistics?

No way of knowing. Remarkable that it's below 2 either way for such a poor country. If they faked it they surely wouldn't have made it lower, so it's possible the real rate is even below that.

Poor countries are usually religious which plays an impact on the fertility rate. The last numbers I saw were 70% of North Koreans are not religious.

Effect of religion on fertility is vastly overstated. Education level of women is the biggest factor.

Pure propaganda, but it's really hard to estimate. At least with China you have some data. Chinese government would say there were 10.5 mln live births in 2021, but there were only 4.6 mln mandatory tuberculosis vaccinations distributed.

Some kids were not vaccinated, you can use a single dose for 2 kids, but that gives you 9.5 mln.

Yet SK has just shy of double the population. NK also has 10 years lower life expectancy, possibly owing to sanctions and constrained food supply