Question How to tweak Shadows with Toon Shading

Hello,
I'm working on a scene with toon shaders in URP, and I'm looking for a way to make "transparent shadows" on my clouds.

To make the toon shaders I followed this tutorial:

I enabled the shader keywords for shadows, but it doesn't seems to react to my shader's 'alpha'.
Does someone know how access and tweak the shadows parameters?

Thank you very much in advance!