How to have only the shadow of an object into its own render layer?

Question

Hello people of stackexchange,

I'm working on a more complex setup but want to understand the basics, so I'll use a simple example.

I have a plane and a cube. The cube is casting a shadow on the plane.

I want the shadow of the cube to show on the plane in the composite, and the cube not to appear at all. The tricky part is that the shadow and the plane must be in different render layers.

I want to obtain the same result as the picture below, but nothing I tried seems to work. I can't seem to get a render layer with only the shadow of the cube:

What I tried:

Render properties > Film > check "transparent"

Cube render layer :

Layer properties > passes > light > check "shadow catcher"

Object properties > visibility > mask > check "shadow catcher"

Object properties > ray visibility > check "shadow"

Cube collection > toggle indirect only

Compositor node setup I tried

I get a white screen in the first one.

I get only the plane in the second one.

Any ideas on how to solve my problem? What am I doing wrong?

Thank you.