Is there a shortcut key in the midi editor that 'zooms to fill'?

… so that when you press it the key editor expands to show every note in the midi part selected to give a visual overview automatically resized to fill the midi window, can’t seem to find one?

If I understand your question, the keyboard shortcut is Shift+F

yep exactly what i want, but within the mdi editor / piano roll - does it work for you there - it doesn’t for me?

Works here triton. Maybe check your keyboard settings in SystemPreferences/Keyboard Keyboard Tab Use F1/F2 etc is what mine is set to. I would check your Key Command in Cubase and see if it is correct

Also Try OPTION+S

Yes, it works for me.