I’m no expert in this area (to put it mildly) but as I understand it just intonation doesn’t fit neatly into a system whereby you can express each accidental as a fixed number of EDOs, because the precise amount by which the pitch is raised or lowered depends on the scale in use. As such, Dorico’s system isn’t intended to handle just intonation.
It is my understanding, however, that you can use Scala files in HALion to provide playback that approximates just intonation, without needing to do anything specific in the host program (whether that’s Dorico or Cubase).