Korea has very high taxes and taxes global income. The government has implemented many restrictions on real estate this year in a bid stop the rapid rise in apartment prices in the Seoul metro area.
Capital gains are not taxes but they will be starting in 2022. The taxes on income, interest and dividends are graduated and the top brackets will exceed 50% once you added in the local taxes. You can search online to find these rates.
Investing in real estate will be difficult and there is risk of fraud unless you know you the Korean system and speak fluent Korea or have a good bi-lingual lawyer you can use for the real estate transactions.
Taxes on real estate gains, especial for apartments are very high and going higher. Given the current government you can expect taxes to go even higher. Also health insurance is based upon your income and your real estate assets, this can result ins some very high premiums. Eventhough the medical services are excellent and inexpensive you will be required as permanent resident to pay for the medical insurance.