Does anyone know if there is a way to insert dynamics for several or all instruments at once?
or at least a function to add a dynamic to all selected notes.
There isn’t yet, Ian. I’ve heard in one of the other places where Dorico is being talked about that it’s on the list of things that’ll come in time.
There is indeed a plan to allow creating dynamics across several instruments at once (which will also edit together). The architecture does allow for that case, and it is currently used by slurs for example.