On Dorico for iPad, the keyboard shortcut for changing voices (the “V” key) only works after having used the software button at least once first. After the software button has been used, the keyboard shortcut works for that staff only. I assume this is a bug.
V is the keyboard shortcut for switching to the next voice; the button in the toolbox creates a new voice. And since you can’t switch to a voice until you’ve created it, it makes sense that the shortcut doesn’t do anything at first.
Voices are created per-staff, which is why the shortcut doesn’t work on a staff even after you’ve created a new voice on another staff.
Edit: Note that the keyboard shortcut to create a new voice is Shift+V.
Ah ha! Thanks. Although you could see how a user could be confused because the onscreen button both adds a new voice switches between the created ones.