You can change the convention of double accidental cancellation in each flow independently; for example, if some flows in your project require archaic cancellation. You can do this in combination with any accidental duration rule.
By default, Dorico Pro uses modern cancellation.
Procedure
Press Ctrl/Cmd-Shift-N to open Notation Options.
In the Flows list, select the flows in which you want to change the double accidental cancellation convention.
By default, only the current flow is selected when you open the dialog. You can select other flows by clicking Select All in the action bar, clicking and dragging across multiple flows, Shift-clicking adjacent flows, and Ctrl/Cmd-clicking individual flows.
In the category list, click Accidentals.
In the Basic section, choose one of the following options for Single accidentals cancelling double accidentals:
To show naturals immediately before single accidentals that come after double accidentals, choose Use archaic cancellation.
To replace double accidentals with single accidentals without showing naturals, choose Use modern cancellation.
Click Apply, then Close.
Result
The double accidental cancellation convention is changed in the selected flows.