Currently, the "Fuse - Configure Joystick" window looks like there is no controller connected even when the controller is connected, and only keyboard keys can be assigned to the emulated Cursor, Kempston, Sinclair 1, Sinclair 2, Timex 1, Timex 2, and Fuller keys and directions.
I suggest evaluating the convenience and versatility of the Steam Launcher key mapping interface, and redesigning the current interface to be more user-friendly and universal.