Cue notes are easy in Sibelius: select a region and you have them in two mouse clicks. I need add cue notes in several projects and haven’t been able to do so. I’ve tried to follow suggestions so far without success.
These steps have always allowed me to input cues:
I’m not looking to copy notes from another instrument. There is only a single vocal part.
Worst case: I will have to add additional players.
Sounds like you’ll have to add a player in order to be a source for the cues. In Setup, make sure this player is not included in the “score”.
Or after inputting the notes, change their size using the Properties panel at the bottom of the window - there should be a Scale size property in the Common group.