A simple Unity example script that makes a UI component track position of world space object rendered with specific world space camera. Canvas needs to be in Screen Space Camera mode.

UIFollow.cs

// A simple Unity example script that makes a UI component track position of world space object rendered with 
// specific world space camera. Canvas needs to be in Screen Space Camera mode.
[ExecuteInEditMode]
public class UIFollow : MonoBehaviour
{
	[Tooltip("World space object to follow")]
	public GameObject target;
	[Tooltip("World space camera that renders the target")]
	public Camera worldCamera;
	[Tooltip("Canvas set in Screen Space Camera mode")]
	public Canvas canvas;

	private void LateUpdate()
	{
		var rt = GetComponent<RectTransform>();
		RectTransform parent = (RectTransform)rt.parent;
		var vp = worldCamera.WorldToViewportPoint(target.transform.position);
		var sp = canvas.worldCamera.ViewportToScreenPoint(vp);
		Vector3 worldPoint;
		RectTransformUtility.ScreenPointToWorldPointInRectangle(parent, sp, canvas.worldCamera, out worldPoint);
		rt.position = worldPoint;
	}
}

Can we do this the other way around? Like the world space object follow the UI object.

Awesome, thanks!