Hangul, the writing system, is the easy part: Jeong In-ji said “A wise man can acquaint himself with them before the morning is over; even a stupid man can learn them in the space of ten days” in the postface to the Hunminjeongeum Haerye. You can learn Hangul easily without interacting with any native speakers, but learning vocabulary, grammar points, colloquialisms, and how to understand dialects would be much more difficult.
Duolingo’s Korean program is decent but not fantastic. The Korean From Zero series (three books with online audio available) is pretty good, and supplementing that with the “Talk To Me In Korean” YouTube channel content and maybe “Learn Korean With GO! Billy Korean” would really help.
It’s also useful to absorb Korean media. Not K-pop — imagine if you learned English by only listening to American rap and pop music, it would be very awkward in actual conversation! — but watching movies, Korean TV shows (dramas and variety shows), etc. can be very informative.