How would one attach one of these fixed microtone symbols to a note?
Change the tonality system to one that includes microtones, then the relevant accidentals will appear in the right panel (in the key signatures and tonality systems tab). See Tip: Change the Tonality System – Dorico for a brief but useful demonstration video.
Yes, microtone accidentals with arrows are all there but the fixed accidentals that are commonly used are not there. See Gould p. 96
Before you place the key signature, you have to edit the 24-EDO tonality system (using the pencil buttton).
Then edit each of the relevant accidentals, deleting the existing glyph and and adding the appropriate one. You’ll find what you’re looking for in the Stein-Zimmerman Accidentals (24-EDO) section.
Thank you