They are still finding crashing bugs related to using Qt QFileDialog native versions especially on Windows.
See this new bug that says how you connect it to the menu that invokes it can cause a crash. but only with newer Windows versions ...
https://bugreports.qt.io/browse/QTBUG-138803
Using "native" QFileDialogs is an issue we may need to address on a platform by platform basis. So adding that env var seems to be the way to go, for users that can accept more crashing behaviour instead of stability.
If it helps, we could probably add a pane that shows an image thumbnail for the selected item to the non-native file dialog much like we have for our own insert Image tool. If we have to move to all non-native dialogs in the future for all platforms, that might be a way to see what an image is without having to first add it.
But creating un-cacheable file thumbnails for each file would really slow down performance in Folders with lots of files.
Caching thumbnails is something better left to the underlying OS.