So far my workflow, in case of keyboard fugues, was to write the voices on separate staves, then merge them into a grand staff.
My understanding is that in Dorico we can copy each voice (staff) and paste it into the grand staff using right click → paste special → paste into voice.
I just want to check whether there is a better way, maybe there is a trick with the condensing feature or some feature I am not aware.
Why not just write the two voices into one stave? Invoke the caret, type Shift-V to create new voices and just V to cycle round the voices that already exist.
So far it is just habit, this way also gave me more flexibility for making changes; a way not to worry about layout. The voices are handled in a very good way, et me just add that the guy at the video tutorial forgot to mention the marvellous “swap voice order” command.