Viewer node shows what I want, photoshop don't

Hi. I am using crypto mattes in order to isolate an asset of my scene and export it with no background.

Here is my setup:

I am mixing the render with a transparent color and using my cryptomatte mask as factor.

When I open the image in photoshop looks empty. Only the checker background.
As a second thing: I can see the buildings in the viewer node also let pass a bit of the checkered background. So they might be a bit transparent, and they should not.

Thank you

Using Crypto passes > Pick your object/material > Set Alpha

Thank you, was not aware of “set alpha” node.