What is atmospheric fog?
Atmospheric Fog gives an approximation of light scattering through a planetary atmosphere. This can give your outdoor levels a much more realistic look. This total effect includes the following: The dominant directional light in your level will receive a sun disc effect in the sky.
Where is atmospheric fog in Ue5?
Atmospheric fog has been deprecated in Unreal Engine 5, you should use Sky Atmosphere instead. Documentation for Sky Atmosphere can be found here. In addition to Sky Atmosphere, you may want to look into volumetric fog which can be found here. I hope this information helps!