Shadow on transparent plane

Questions
1

Is it possible to create a plane on which only shadows from objects can be seen? Will shadows appear, for example, on a plane with 0 opacity?

2

Yes you can use a plane to only receive shadows.
https://codepen.io/Fyrestar/pen/QOXJaJ

3

Thanks Fyrestar.
I just discovered ShadowMaterial as well.

4

There are even more examples in the collection with links in the code.

For shadows see eXtended eXamples