Comment by ToFab123

Afaik the Win3 file dialog gets called up by some old apps that use old APIs. I think I even ran into it in Wine.

The analog in Unix apps are GTK's file dialogs, which always look jarring and out-of-place anywhere other than Gnome (and maybe XFCE and KDE, dunno)—making me feel like I stepped into 90s Unix with those Motif-derived concrete slabs. Plus they're un-integrated with non-Linux OSes, missing features. And the dialogs keep being dragged around by GTK apps—open Gimp on Mac or Windows and there you go: GTK dialogs.