I found this polygon article that explained it (I scrolled down to the "Good, Bad, and Very Bad" section because I don't care to get too deep into it tonight lmao).

It sounds like the writer definitely holds nationalist, anti-Korean thoughts and some themes in the manga/anime can be compared to antisemitic conspiracies. That sucks. I only watched the first season of the show (and I can't remember how it ended), and I never got to the part about the Eldians and Yaegerists, so that stuff is completely unknown to me.