[atoav]

A thing that "always works" is outputing the transparancy as a grayscale (black=transparent, white=opaque) alpha video. You can combine these in an after effects composition which you can load directly into Premiere: https://helpx.adobe.com/premiere-pro/using/compositing-alpha...

The output of that tool also looks suspiciously like a so-called cryptomatte which many 3D tools use to store masks for each of the objects/materials/etc, Blender can read and write those — although I am not sure whether this tools supports outputing those.

[RoseyWasTaken]

Exactly this! I experimented with a depth estimation model. An image was added as an input, the output was a depth map in grayscale, which I later used in Photoshop as a mask for Lens-blur simulation.