The following patch should fix this issue. Could you please try it out?

Index: NoesisView.cs
===================================================================
--- NoesisView.cs	(revision 16730)
+++ NoesisView.cs	(working copy)
@@ -1319,10 +1319,6 @@
     {
       #if ENABLE_LEGACY_INPUT_MANAGER
         Vector3 mousePosition = UnityEngine.Input.mousePosition;
-      #else
-        Vector3 mousePosition = UnityEngine.InputSystem.Mouse.current.position.ReadValue();
-      #endif
-
         Vector3 p = Display.RelativeMouseAt(mousePosition);
 
         if (p == Vector3.zero)
@@ -1332,6 +1328,11 @@
 
         _activeDisplay = (int)p.z;
         return p;
+      #else
+        Vector3 mousePosition = UnityEngine.InputSystem.Mouse.current.position.ReadValue();
+        _activeDisplay = UnityEngine.InputSystem.Mouse.current.displayIndex.value;
+        return mousePosition;
+      #endif
     }
 
     private void UpdateMouse()

The implementation of MousePosition should be like this:

    private Vector3 MousePosition()
    {
      #if ENABLE_LEGACY_INPUT_MANAGER
        Vector3 mousePosition = UnityEngine.Input.mousePosition;
        Vector3 p = Display.RelativeMouseAt(mousePosition);

        if (p == Vector3.zero)
        {
            return mousePosition;
        }

        _activeDisplay = (int)p.z;
        return p;
      #else
        Vector3 mousePosition = UnityEngine.InputSystem.Mouse.current.position.ReadValue();
        _activeDisplay = UnityEngine.InputSystem.Mouse.current.displayIndex.value;
        return mousePosition;
      #endif
    }

Hi and sorry for the late feedback.

We did some first tests and it looks promising. But so far it only seems to work in standalone builds which makes it a bit tricky to use for development.

The mouse z is the index of the screen and that doesn't work in the editor.

If you open a second game screen in Unity and set that one to Display 2 the mouse display index (z) will still return Display 1 the entire time.

This would be probably helpful to be added or used to get the right one in editor mode: https://docs.unity3d.com/6000.3/Documentation/ScriptReference/Display-activeEditorGameViewTarget.html

The main issue we have in the editor is that OnGUI is not invoked on secondary displays. The proper solution would be to deprecate OnGUI entirely. This is something we’re considering for Noesis 4.0, but I can provide you with a preview in 3.2 (disabled by default) so you can try it out.

It appears that click events are properly handeled now, we are able to click the buttons and open menus on the second monitor. However mouseover items such as tooltips and style changes appear to only work after an item has been clicked. It also appears to work only for the item that is cliucked. In the attached image the tooltip and red highlight appear only once the button is pressed, and not for any of the other buttons until that particular button is clicked. The Mouseover function appears to persist only while the mouse remains over the item post click.

And yes @jsantos, I'd be interested in that preview in 3.2.

Just to confirm, the issues are in the Editor only, right? The runtime always works fine?

No those issues above are indeed happening in standalone builds.

About that preview: Is there a way to get hands on it? Thank you!

Hey Xaron, we have been really busy with the imminent release of 4.0.

I will try to find time for this as soon as possible.

I wanted to have this for 4.0, but unfortunately, we didn't have time for it. This will be one of our priorities for 4.0.1.

Thanks for your patience!