HDRP vs Post-Processing

yo dude just look here:
https://docs.unity3d.com/Packages/com.unity.render-pipelines.high-definition@6.5/api/UnityEngine.Experimental.Rendering.HDPipeline.VolumetricFog.html

and the code example here:

There also might be some naming missmatch of the parameters. Like it says “Base Fog Distance” in inspector but in code this parameter is called “meanFreePath”.