Permanent handles (when object is not selected)

I was digging through the internet to find solution for this, and here it is: in custom inspector, add handle-drawing function to SceneView.OnSceneGUIDelgate. Something like this:

         private void OnScene(SceneView sceneview)
         {
             // draw handles
         }
         
         void OnEnable()
         {
             SceneView.onSceneGUIDelegate -= OnScene;
             SceneView.onSceneGUIDelegate += OnScene;
         }

Now OnScene method is called with each sceneGUI event, whether or not gameObject is selected, and Handles are enabled and movable.

btw - if handles don't move in OnScene(SceneView), try simply calling OnSceneGUI() from OnScene(SceneView) (you still need OnScene, for this delegate passes SceneView as an argument).