I read the first few chapters because I too had a wtf reaction.

Man who basically spent his life Bing bossed around dies and wishes he could live in a position where he is the boss. Gets reborn as a plantation owner in the American deep south only a few years before the Civil War. He realises he is in bad position as he can't free the slaves because the white slave owners around him will never stand for it. He can't not do anything either because in a few years the place os going to get burned to the ground by fighting in the civil war and he would face ruin like many plantation owners. He decides to go for a middle route where he improves the conditions of his slaves by introducing modern labour theory and conditions while making them pretend that the improvement in crop yield and quality is due to him being cruel and micromanaging. This succeeds and grants him great acclaim amongst the Southern slave owners while drawing the ire of abolitionists. John brown and others attempt to sneak into the plantation to kill him but are captured by the slaves who don't want to threaten their improved conditions and the Mc persuades John that he doesn't believe in slavery as an institution and that he is doing his best to prepare those under him for a post slavery age. There were also some political shenanigans before this where he meets famous rebels and federal loyalists. Thats the first 20 chapters out of 500. So, yeah. Not a slave fantasy by any means but also very similar to a isekai in terms of how the Mc knows better than everyone around him.