There are a ton of legal websites offering free-to-watch Korean drama. For instance, YouTube, Naver TV, Tubi, iFlix, IQIYI, and WeTV all allow you to stream popular shows without paying (though you will have to watch ads).
If you’re willing to pay a little, there are even more options. Netflix has a ton of K-Drama, from the platform’s most popular show of all time, Squid Game to classic Crash Landing on You. Other services, such as Amazon Prime Video, KOCOWA, and VIU, may be an option too, depending on where you are in the world.