In this tutorial, David from Lightning Boy Studio shows how to create volumetric clouds in the style of Ghibli films in Blender 2.9.
When it comes to big puffy clouds in 3D, one technique that could be used is volumetric effects.

Also, check another tutorial bt David about to create the trees in Ghibli style, tutorial + file project to download for Blender scene.

In this tutorial, we will look at how to create Ghibli-style clouds with flat planes and smart shaders.

The tutorial covers creating clouds in cartoon anime style, using normal maps, and some shader tricks to get a result that looks very much volumetric.

How to Create Ghibli Clouds in 3D in Blender?

Shader/Tutorial Ghibli anime-style clouds for blender

Source files for this tutorial on Ghibli clouds, feel free to download!
This is a procedural shader for achieving 2D clouds in a ghibli style.