https://english.visitkorea.or.kr/enu/AKR/FU_EN_15.jsp?cid=2818913
From June 1, 2022, travelers are allowed to enter Jeju and Yangyang visa-free via international airports. The visa-waiver program, which allows international travelers to visit Korea short-term without the requirement of visa, was suspended since June 1, 2020 as a precautionary measure against COVID-19.
Although most international travelers will be allowed to enter Jeju Island visa-free, exceptions apply. The visa-free entrance to Jeju does not apply to citizens of 24 countries/regions* and 10 other countries** that have mutually suspended the visa-waiver program with Korea (Japan, Hong Kong, Taiwan, Macau, etc.).
As for Yangyang, only groups of 5 or more travelers from Vietnam, the Philippines, Indonesia, and Mongolia (effective October) can enter visa-free. To be waived of visa requirement, the group tourists must travel to Korea through a designated travel agency.
* Countries/regions that require a visa to enter Jeju International Airport: Iran, Sudan, Syria, Macedonia, Cuba, Kosovo, Palestine, Afghanistan, Iraq, Ghana, Nigeria, Yemen, Egypt, Gambia, Senegal, Bangladesh, Kyrgyzstan, Pakistan, Somalia, Uzbekistan, Nepal, Cameroon, Sri Lanka, Myanmar
** Subject to change; for further details on visa eligibility, please check with the embassy or consular offices of your country in Korea.