This procedural cloud is made using blender 2.91’s ability to convert meshes into volumes. You can customize this cloud super easily: simply create a rough cloud shaped mesh, select volume object, and set its first modifier’s object field to your cloud shaped mesh. That’s it! Don’t forget to hide your cloud shaped mesh from the render. The volume displace modifier is then used to make the volume look cloud-like and natural (this is already set up).
Nishita Sky Environment Texture and cloud texture are already set up and ready to go. The compositor also has the denoising node set up to make rendering super fast!