The best strategy would be to schedule a meeting so that we can explain what we learned about that High-DPI stuff on macOS. My best guess would be that window sharing in Virtend needs a small adjustment because it fails to recognize that "backing scale factor" stuff Apple introduced.

This attempt here looks like you are trying to fix the wrong end of the problem. Yet, I will double-check now whether we made a mistake in `ioSizeOfWindowSetxy`.