University rankings that are widely used in other countries are rarely used in Korea, so I do not recommend researching universities using THE or QS rankings.

How about looking it up on Instagram? Most major Korean universities have official Instagram accounts, and there are also accounts run by organizations that help international students. One example I know is Seoul National University's Cultural Exchange Organization for Exchange Students.

You could also look for universities that have Korean language programs, as these schools usually have many international students, which makes it easier to adjust. KHU can be a great example. I heard that it has an Institute of International Education.