You need to add the HUD asset in the Asset Browser to a camera or a scene. Only then, you can add a HUD element to the HUD asset and display the information in the element in the Viewer.
To add a HUD asset to the active camera or the scene:
The HUD asset added to the current camera acts as a parent to the HUD asset added with it in the scene.
If you try to add a second HUD asset to the current camera, then the Replace Current Camera's HUD option appears in the contextual menu.
Selecting this option replaces the HUD asset in the current camera, and adds another HUD to the scene. In this case, the name of the replaced and added HUD assets is HUD 1.
To add a HUD asset from the scene or a camera to another camera:
To delete a HUD asset from the scene or a camera:
If the HUD asset in a camera is a parent of another HUD asset in the scene and vice versa, then both the HUD assets are deleted.
To detach a HUD asset from a camera:
The <camera_name> displays the name of the camera to which the HUD asset belongs.
Selecting the Detach HUD From <camera_name> option detaches the HUD asset only from the camera, even though it contains a child HUD asset in the scene.