This is intended behavior. Source and destination need to have the same number of MSAA samples. From the documentation: "The data in the texture is copied pixel by pixel. The copy function can only do 1:1 copies it will not allow scaling the data or doing texture filtering. Furthermore it requires the source and destination surfaces to be the same size in pixels and have the same number of MSAA samples."
User code manually sets the destination to have no MSAA samples regardless of the source format.
More information: https://docs.unity3d.com/Packages/com.unity.render-pipelines.core@17.1/api/UnityEngine.Rendering.RenderGraphModule.Util.RenderGraphUtils.html