This is a paid asset, but now you can download GaussianBlur_HDRP Free.
Detail this asset from Unity Store: Original Link
GaussianBlur_HDRP v1.0
GaussianBlur_HDRP
* Demos for UI and 3D Objects
Note: If you use this asset in your game, please put my name in the credits.
These materials use a lot of the assets that come with the HDRP ExampleAsset, therefore please make sure you have that in your project before adding this asset.
This demo shows off how the GaussianBlur_HDRP.material looks when attached to a 3d objects.
GaussianBlur_HDRP_Controller.cs
this script controls the blur, however you might want to use your own script in your project.
createRenderTexture.prefab
creates a second camera with a renderTexture, and sets it in the materials. the scene can work without this if you set up a second camera manually.
This shows off both types of materials in the HDRP Example Scene.