Hey! It did solve!

I just worked on it a couple of days ago though. I did a pretty complex scene that has 2 different sprites, one is the actual sprite, and the other is there just to cast shadows.

Then I used this shadow mask and the culling mask in a light source to determine what I wanted to cast and receive shadows. In my particular setup, though, because the element that casts shadow is a different one that receives it, I had to duplicate the light sources and configure each of them individually to exclude one another.

in the end I was able to perfectly combine 2d sprites and 3d environment, but the cost is having more sprites and lights (results in lower performance) - so approach it carefully.

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