For an average U.S. citizen without any other citizenship, it must be legally permissible to visit for tourism reasons. Neither North Korea or the USA should have any laws against it.

The question pertains to the primary territory of present-day North Korea [2024]. Any alterations in names, political dynamics, or border adjustments will not affect the resolution of the question. If North Korea splits up, the largest split (by territory) will be considered as North Korea in the future.

It was prohibited by the U.S. in 2017. North Korea recently opened their border for Russian tourists. For more information: https://edition.cnn.com/travel/north-korea-tourism-reopening-intl-hnk/index.html