Speaking to NK News, Hong Min, director of the North Korean research division at Korea Insitute for National Unification, stated, "Her disappearance could be due to coronavirus pandemic. As a mother with young children, participating in public activities risks potential infection. Even Kim Jong-un went on the lowest number of on-site guidance in the past year."

source https://zeenews.india.com/world/north-korean-dictator-kim-jong-uns-wife-ri-sol-ju-for-over-a-year-conspiracy-theories-surface-on-internet-2339074.html