You can stop looking – and it isn’t a software mistake.
The DI units (788ci D among them) does not have this menu because there is only one transducer type that works with this transducer: the DI transducer (either the transom, inside-the-hull or trolling motor version).
The 788ci DI unit was never meant to work with the QuadraBeam transducer but the (non-DI) 788ci unit is and has that menu.