NEW! Now You don't need Blit script. Unity 2022+ have build-in Fullscreen render feature. Therebefore it's better to start from from "Edge detection shader".
But I will left this old information:
Blit script: https://cyangamedev.wordpress.com/2020/06/22/urp-post-processing/
Screen position to World position: https://forum.unity.com/threads/computing-world-position-from-depth.760421/
More useful information: https://realtimevfx.com/t/death-stranding-odradek-terrain-scanner-ue4-case-study/11200