8va underneath an upper stave 8va - Dorico refuses

[pianoleo]

No, you just need to use the caret:

@Lillie_Harris

When you have cross-staff notes, you need to input the octave line either from the caret (i.e. activate the caret, make sure it’s on the top staff, and input the octave line with the caret active, making sure you press Space after input to give it duration and make it appear) or input it on the bottom staff and move it to the staff above.