As far as I understand, MuseScore supports common key signatures, but not full-blown scales, because for that it would need to understand two more things, namely...
- Root notes
- "Key signatures" that don't follow the usual circle of fifth pattern (think melodic and harmonic minor, maybe blues notes (note sure if these are handled as separate scale degrees or "inbetween" from a theoretical PoV), and wilder animals like symmetric scales).
An understanding of these two concepts would allow MuseScore (or plugins thereof) to do a number of cool things. Off the top of my head :
- When you type in a note name in note input mode, the defaut alteration could be correct even in more exotic scales like harmonic minor.
- Roman numeral analysis could be less manual (e.g. you type a degree, and it automatically determines the standard chord quality for that scale and degree, or you type a note name and it automatically turns that into a degree and standard chord quality)
- Roman numeral analysis could be better integrated with chord symbols (you change one, MuseScore adjusts the other, and given an RNA, MuseScore can generate basic chords matching this RNA for you)
- Out-of-scale notes could be automatically highlighted (some DAWs do this and it does wonders for composers who are getting started with a new scale and learning to stay in the scale or depart from it purposely)
I pointed this out in Marc Sabatella's course, who replied that in his opinion, this could be handled by a plugin. I don't know enough about MuseScore plugin development to assess how correct this is (it seems to me that you would need to somehow save some extra information in the score file, but maybe plugins can do that ?).
I tested this in 3.6, but am not sure if this is still true as of current MuseScore 4 nightlies, which seem to possibly understand minor now judging by its evocation in the "new score" dialog. However, without extra documentation, I couldn't tell if this is just a more convenient way to select key signatures or if this reflects a deeper departure towards full scale support.