HDR data is not rendered into render texture when using URP

I'm trying to do a similar thing in unity 2021.2.15f (latest unity version at the time) using URP.

I've got a sun (sphere) with a material with a HDR emissive colour with an intensity of 10, I render this to a cube map using this code:

 public class CubeMapGenerator : MonoBehaviour
 {
     public Camera Camera;
     public RenderTexture RenderTexture;
     public GameObject Background;
     public Material BackgroundMaterial;
 
     void Start()
     {
         RenderTexture.format = RenderTextureFormat.DefaultHDR;
         Camera.allowHDR = true;
         Camera.RenderToCubemap(RenderTexture);
         Background.SetActive(false);
         BackgroundMaterial.SetTexture("_Tex", RenderTexture);
         RenderSettings.skybox = BackgroundMaterial;
     }
 }

I then place the rendered texture into a Cubemap material and apply as my skybox and add post effects with bloom threshold of 1.0.

There is no bloom effect, it suggests there's no values sorted above 1.0 in the rendered texture colour channels, my sun object (still sitting in the scene) glows dramatically as expected.

Is there something I'm missing I've tried all the format options including R32G32B32A32_FLOAT.

I've made a demo project of this which I can put into a GitHub repo if that helps.

Found solution. Updated my question with the answer!