I'm on the last wish quest, and have found the Djinn, but immediately when I start battling it, it one shots me, I tried putting the dificulty all the way down to "Just The Story!" but that did not work either.
Do you have enemy upscaling enabled in the settings? That's notorious for making the djinn insanely strong.
Or, are you using any mods?
Or, are you using any mods?