Using digikam 5.6.0 I am able to export shortcut schemes. (Menu: Settings→Configure Shotcuts…→ Manage Schemes» → more Actions → Export Scheme)

This results in an extension-less file (contents in typical ini format)

However: How do I import back in again? The shortcut-Filter of the file dialog filters down to something, but I simply don't know what extension... no luck with guessing...