How to add transparent background to scene capture 2d?

Hello. I’m trying to add transparent background to scene capture 2d. The problem is I’m using post processing so I need to use Final Color (LDR) for scene capture. But in my material I don’t have anything (as I think) in alpha channel:
image
I’m using “before tonemapping” in post processing materials. Always persist rendering is enabled. How can I fix that?