This is a paid asset, but now you can download Volumetric Clouds Free.
Detail this asset from Unity Store: Original Link
Volumetric Clouds v3.5 (Latest version)
“If possible, please buy the package to support the developer”
Volumetric Clouds is a fullscreen shader which uses raymarching through a texture to render fully 3D clouds on screen.
This package contains the following :
-A shader and a cginc file
-A C# script to attach to a camera and another one to fire events linked to clouds
-Two materials, acting as presets for low and high quality
-A bunch of editor scripts for the material inspector
-An offline manual
-Four texture variant
HDRP & LDRP not supported yet.