How to make the main window non-resizable when a popup is open/visible?

[qarmin]

When I open a popupWindow in Slint, I can still resize the main window, which causes the popupWindow to stop responding to button clicks after a while.
It looks like this issue has existed for at least a year, so there's little chance it will be fixed soon, and I'm looking for a workaround.
I figured that preventing the main window from being resized while the popupWindow is active could be a good solution.
However, is this possible to implement?

[ogoffart]

Ideally we'd have support for actual popup window in winit so we could implement that at the window manager level. (rust-windowing/winit#403)
Failling that, we could indeed try to work around it by having something in the winit backend that prevent resizing when a popup is open. (actually, it should incercept click outside of the window to behave like a native popup)
But this is not yet implemented.