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](https://en.wikipedia.org/wiki/INI_file))

**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...

[![enter image description here][1]][1]

**Update**

At least, there's a workaround: past full, absolute path (inkl. filename) into the Location field at top, press import. Works...

  [1]: https://i.sstatic.net/VrJu9.png