MACOS problem with ANY C++ GUI Window

Brighter3D

I am using Fiddle to run C++ GUI code from SketchUp Ruby,
on Windows everything is fine.
On MacOs I found a problem I can not solve by months.

After window is shown (by first toolbar button) for the first time and closed
most of the SketchUp "Window" menu items get disabled.
It gets disabled right after window is shown and do not get enabled anymore (even after window is closed).

It looks like this:
Problem screenshot

Also when you try to do the same again (show window) by the same first toolbar button, window is not shown again, and there is no button event on the ruby side (even when you click the button).

It looks like a SketchUp is broken in some way by using c++ GUI window (event loop maybe?).
It happens not only with FLTK but also with other GUI's like:

Coocoa
OpenGl
Nuklear
ultralig.ht

Minimal test plugin:
Test plugin

XCode source:
https://drive.google.com/file/d/1exFrLjjPIBqwQA3XfsPQCIjVgltV8qLO/view?usp=sharing

Any help is appreciated...