I've got some weird line were i think fog should be
at a certain point above the camera (relative) there is this line where the fog just ends (visible at the mountain in the distance). i've got some mods active but i dont think they got anything to do with it. I also tried to find a solution by searching through this discord and found some report that iris got a problem. other than that i got no idea how to fix it.

Solution
if the DH LODs don't have fog and you did not disable it, some mod is telling DH to turn it off
Iris is known to do that, so if you want fog without shaders, remvoe Iris if you use it
Iris is known to do that, so if you want fog without shaders, remvoe Iris if you use it