I think you probably need [GVfs](https://en.wikipedia.org/wiki/GVfs) for that to work. I don't know if it works on Macos, but if so it should probably be bundled in the [OSX build](https://github.com/geany/geany-osx), and if not, the [`GtkFileChooser`](https://developer.gnome.org/gtk3/stable/GtkFileChooser.html) should probably set [`local-only`](https://developer.gnome.org/gtk3/stable/GtkFileChooser.html#GtkFileChooser--...) to `TRUE` on the platform to hide the missing functionality.