Unity3D Editor OnSceneGUI() code for detecting mouse-press while key held changed in 2020.2.7f1 (at least)

ButtonAndMouseInEditor.cs

using UnityEngine;
#if UNITY_EDITOR
using UnityEditor;
#endif

// pre C#8
//#nullable enable

public sealed class ButtonAndMouseInEditor : MonoBehaviour {

	[SerializeField]
	internal KeyCode key = KeyCode.A;

}

#if UNITY_EDITOR
[CustomEditor(typeof(ButtonAndMouseInEditor))]
public sealed class ButtonAndMouseInEditorEditor : Editor {
	public void OnSceneGUI() {
		var actual = (ButtonAndMouseInEditor) target;

		// focus on SceneView.  Assumes only 1 open
		if (EditorWindow.mouseOverWindow is SceneView && !(EditorWindow.focusedWindow is SceneView)) {
			EditorWindow.FocusWindowIfItsOpen<SceneView>();
		}

		switch (Event.current.type) {
			case EventType.MouseDown:
				if (keyDown) {
					Debug.Log("MouseDown WHILE key is held = success (remember to click back on object with this class)");
				} else {
					Debug.Log("MouseDown while key is NOT held (remember to click back on object with this class)");
				}
				break;

			case EventType.KeyDown:
				if (!keyDown && actual.key == Event.current.keyCode) {
					Debug.Log("KeyDown");
					keyDown = true;
				}
				break;

			case EventType.KeyUp:
				if (keyDown && actual.key == Event.current.keyCode) {
					Debug.Log("KeyUp");
					keyDown = false;
				}
				break;
		}

		var overWindow = EditorWindow.mouseOverWindow;
		var focusedWindow = EditorWindow.focusedWindow;
		Handles.BeginGUI();
		const int NumLines = 4;
		GUI.Box(new Rect(0, 0, 400, 20 * NumLines), string.Format("ACTIVE!\nkeyDown:{0}\nover:{1} (SceneView:{2})\nfocus:{3} (SceneView:{4})", keyDown, overWindow, overWindow is SceneView, focusedWindow, focusedWindow is SceneView));
		Handles.EndGUI();
	}

	private bool keyDown;
}
#endif // UNITY_EDITOR