N3rdTek I'm not sure where you heard that call screening was removed from GrapheneOS for privacy reasons, but that doesn't sound right.
To be perfectly honest, I'm not sure whether Pixel exclusive features like call screening work on GrapheneOS or not.
If the feature has a hard dependency on code within the stock Pixel OS that is not included with AOSP, then it's unlikely to work on GrapheneOS. However if the functionality depends only on the Google apps and finessing of their permissions, then it should be possible to enable them on GrapheneOS. I see nothing in GrapheneOS that would block such features from working, other than dependency on code that is not available through AOSP.
I'm not a developer, and don't currently have anything better than trial and error to try and enable Pixel exclusive features with Google apps. Please feel free to have a play around and see where it takes you!