Therefore, Alx Sa has begun porting GIMP’s file choosers to the “native” option provided in GTK3. This means that when you open or save a file, you will see your platform’s standard file chooser dialog instead of the GTK dialog (unless your platform uses that already, in which case there will be no change!)
Ironic that GIMP itself is moving away from the GIMP ToolKit file chooser dialog, LOL.
(For those who aren't aware, GTK was created for GIMP and was only subsequently adopted by other projects like GNOME.)