In Unity 6, URP now has a setting for Alpha Processing (URP Asset > Post-processing > Alpha Processing). With this enabled, URP will process alpha when rendering the post processing stack as opposed to discarding it (replaced alpha values with 1 before).
The render target requires a format with the alpha channel. The camera color buffer format must be RGBA8 for SDR (HDR off) and RGBA16F for HDR (64-bits). You can configure the format using the settings in URP Asset > Quality.
If you use HDR and don’t see the HDR Precision settings, you need to click on the three dots on the top right and enable “Show Additional Settings”.
We are working on samples to show how to use this option for several use cases.