I made fog sphere in post process and i need to make all black transparent, in post process material isnt possible to change blend mode, how to make this?
That’s not how PostProcess work.
Think of it as some video editing software, like After Effects or Nuke.
The emissive color is your final output image.
To add overlay, you need to get your “preprocessed” image and add effects to it.
You may use different nodes, but generally that’s - SceneTexture:PostProcessInput0
To blend Anything you will need to use any of the Blend nodes (there are many), ore using the math they are based on.
For adding a mask of a material, you may need a CustomDepth channel as well.
This is just an example:
More here: Post Process Materials | Unreal Engine Documentation