The Shadow Catcher in Blender allows shadows to exist visually without the plane receiving them being visible in the final render.
What is it used for?
It is mainly used in renders with alpha (transparency), when the goal is to compose the 3D model over another background (for example, in post-production or product design) without losing the light and shadow interaction that gives realism to the scene, or when we want to have the object with alpha but also with its shadow (for example, for creating 360º visualizations).
How to apply it?
a) Create the shadow-catching plane beneath the object.
b) In the Object Properties panel → Visibility, enable the Shadow Catcher option.
c) Make sure the render is set up with Film → Transparent in the world properties, so that the background is transparent.
d) Render with Cycles.
In previous versions, this was enough. We would save the png and it would already come with shadows, but now it is necessary to apply the following configuration in the compositor.
Now we save in .png or .tiff and we have the image with a transparent background and shadow.
If the goal is to integrate the object into a real photo, it is essential that the lighting of the scene is as even as possible to the lighting of the real photo.