Painting on top of my bake and exported only what's painted?

Hello, let’s say I have a baked texture and I want to paint on top of it some additional things.
So I go to 2d texture view, do my painting. All good so far!

But now, I need to export ONLY those thing I have just painted with transparent everything else. How to achieve this?

In Photoshop I would simply create two layers, one with my original bake and another where I do my painting. Then export only the top layer leaving the background transparent.

How to go with the same workflow in Blender?

Thank you!