This application has a proof of concept to register a folder appropriately with macOS' Launch Services. It has been tested with Qt 5.12.1

The application just displays a string Info: Nothing set if it was opened normally (This is the only behavior that will happen on Windows), and will display the full path to the associated file, if it was open by double clicking a registered folder.

The registered folder has the extension macoscrashtest, since this was originally created to test a crash.