Previous Visa excempt countries require the Korean ETA starting in September 2021. If your Country is on the list above you have to apply for the Korean ETA before you embark on your journey to South Korea.
The K-ETA intends to further secure South Koreas borders and streamline the entry process.

Many factors determine whether a country will be considered for visa-free entry. The government must be assured that there is a low risk of security threats coming from visiting citizens of the said nation, so positive diplomatic relations with South Korea are a base requirement.

New Eligible Countries will most likely be added to the South Korean K-ETA program as new diplomatic ties are forged. For example, the UAE was added to the list a year after the strengthening of the relationship between the two countries under the 2022 Abraham Accords.

Once on the ETA for Korea list, eligible countries are expected to stay on the list. Only in extremely rare cases eligible countries are rescinded.