Steps to reproduce:
- Open "OutdoorsScene" in the attached project
- Look at the rendering
- Change the shadow max distance in the "Sky and Fog Volume"
- Observe
- Disable the Sun shadows
- Observe

Expected : The rendering of the volumetric fog should not be affected by the cascade shadow distance.

Notes:
It seems to be only due to the cascade shadows. If you place a point light in the scene and disable the sun shadows, the fog if fully visible and the light is affecting it properly outside of the shadow distance range.

Reproductible with:
- Unity trunk & HDRP master branch
- Unity 2021.2.4f1
- Unity 2020.3.22f1 & HDRP 10.7.0