HandleUtility is an editor class! You should only use it inside the UnityEditor, and inside of a folder named ‘Editor’ so that the compiler knows not to include it when trying to build a standalone. For the same functionality, you should be using Camera.main.WorldToScreenPoint (with some transformations)- it functions using the main camera instead of the ‘scene camera’- an invisible, intangible camera which the Editor uses to render the Scene View.