Well, apparently some users still have issues with this new FileChooser implementation, the window is not showing when it is created with a non-existing file path as the initialFileOrDirectory argument. This time, it is not related to unicode, this is just an issue triggered by the fact that the supplied folder does not exists. Unfortunately I cannot reproduce it, I have Windows 10 ver 2004. But it is confirmed to happen on the computer of a user having Windows 10 ver 1909.
When I revert the recent changes of the FileChooser by commenting the lines :
if (SystemStats::getOperatingSystemType() >= SystemStats::WinVista
&& customComponent == nullptr)
return openDialogVistaAndUp (async);
it fixes the issue on his computer. So for now, I am going to do the same.