Back in 2017 if I remember, the premium was 10%-20% for month after month, with billions being traded. Some people must have made a
lot of money by knowing how to convert large sums of KWR back to BTC (presumably via USD).
My guess was by exporting electronics or something similar. USD -> US exchange -> BTC -> KR exchange -> KRW -> electronics -> ship to USA -> USD. Of course a very friendly banker might provide an easier route.
Non-Koreans can't trade on Korean
crypto exchanges any more (but maybe can own a Korean company that does?). Iran and Venezuela seem to have a premium for obvious reasons, but again it's hard to trade the loop.