Enharmonic trills

Dorico wont show a trill to the the same pitch unless you do a notehead change to the auxiliary note first. Make sure to have trill appearance set to “auxiliary note” either in engraving options or the properties panel. Then choose any other interval than a unison. Select the pitch, go to Edit-Notations-Notehead and change to “Default Noteheads”. Then you should be able to make the auxiliary note appear when choosing a unison.

In Dorico 3.5 and previous versions, you could access the notehead sets through the context menu, but in Dorico 4 you have to go through the menu line and edit menu on the top of the screen. There is options for setting specific noteheads through custom key commands.