We are middle of upgrading our project to HDRP and we noticed some unusual behavior regarding RenderTexture. We a very basic avatar displayed in our UI using RenderTexture into an ImageSource using TextureSource. This was working perfectly before switching to HDRP. But since upgrading, the alpha is not respected. I verified in Unity, and the alpha channel is properly set and when using it in a raw image, the transparency is correct but in NoesisGUI, the transparency is no longer applied. Any idea what could cause this ?

Solved by changing the background color on the camera to 0, 0, 0, 0

Great! I was going to work on this now, thanks for saving us time.

For anyone else having issue, also make sure in the HDRP quality settings to set R16G16B16A16 as Color Buffer Format.

I will improve the documentation and verify. So R8G8B8A8 is not working?

This in the HDRP settings in the Color Buffer Format. The only possible values is R11G11B10 or R16G16B16A16 .
Even if the texture is declared as R8G8B8A8, it will not work if the HDRP settings does not include alpha.

I see, thanks for the clarification!