If you want to quit your job, just bet on 2 million KRW in monthly dividends

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It doesn't necessarily have to be dividends; if you have something like a building or some other source that brings in about 2 million KRW a month even while you're doing nothing, it might be better not to work a high-stress job.
Of course, the conditions here are being single and giving up on living in Seoul. Some people bring up health and medical expenses, but honestly, unless you are truly elderly, if you take care of your health while not working, you won't get sick easily. People get sick and go to the hospital because they work, get stressed, and then relieve that stress with alcohol, smoking, or greasy food. Usually, when people quit their jobs, even existing ailments tend to heal. There's a reason why being unemployed is considered a good fate. If you are unemployed using your own money, there is nothing morally wrong with it. Though, honestly, who even cares about that kind of thing these days?
To be fair, if you care about dignity and such in your 40s or 50s, it is true that living on that amount is tight, but for an ordinary person, being overly conscious of how others see you is a foolish way to live. So, if you just hate working to death, you can set up about 2 million KRW in monthly dividends and quit.
From age 65, even if you started working in your 30s but quit in your early 40s, you would have likely met the minimum 10-year contribution period for the National Pension, so you'll get at least a little bit of pocket money from that too.
If you occasionally find yourself a bit short on cash, you can just do some work as a designated driver or for Coupang. You don't even have to do it much—just for exactly 7 days. Since National Pension and health insurance premiums are deducted starting from the 8th day, you can work just those 7 days, or even less if you don't want to work.
Of course, if you want that 2 million KRW to be a very absolute minimum, you would need a principal of over 500 million KRW, but if you decide to fill it only with covered calls that carry the risk of principal loss, it is possible with 200–300 million KRW (though I do not recommend this route).
It is all your own freedom.
If you get married, you can never choose this lifestyle. But if you live alone, I think it is definitely worth trying. If you had more money, it would be nice to support your parents, but given today's reality, just taking good care of yourself without getting into trouble is filial piety enough.