I'm not feeling well but perhaps the following screenshots and checklist that I've just cobbled together will give some clues. Make sure HD pipeline is working. Make sure Volumetric Fog and Volumetric Lighting Controller are added to scene settings via 'Add component overrides...', and that boxes next to options in these components are ticked (eg by pressing All). Make sure Volumetric is selected in Scene Visual Environment Settings. Default Mean Free Path is a very high number - either make this number very low to see the fog clearly, or create a new gameobject and attach a Density Volume component to it, scale and position the gameobject appropriately, play with Mean Free Path setting in this Density Volume.