Hello, Noé.

Thank you for looking into it! So, it is not a bug. I copy another user
who reported having the same difficulty in guix-help mailing list.

On Thu, 20 Feb 2025 00:26:39 +0100
Noé Lopez <noe@xn--no-cja.eu> wrote:

> The glyphs are indeed not showing if the selected font is Edwin (the
> default), but if you select a font like Noto Sans, or DejaVu Sans for
> your text the characters will appear fine. It seems the “special
> characters” window uses the selected font for previews.

If I select FreeSerif instead of Edwin in the side panel before clicking
the "Insert special characters" button, I achive the expected result later
in the "Greek Extended" tab. With FreeSerif, most of the characters are
displayed with only a handful of glyphs missing. FreeSerif is budled in
the musescore package, so it is readily available.

If I install the font-google-noto package and restart MuseScore, I can
also select Noto fonts. I tried Noto Sans and Noto Serif. They appear to
be missing the same glyphs as FreeSerif. So, it is not necessary to
install Noto fonts.

In Trisquel, the pre-selected font is FreeSerif instead of Edwin. There
is no package for Edwin font in Trisquel. However, I downloaded the font
from its git repository, installed it in Trisquel, and observed exactly
the same result as in Guix, which is most of the glyphs missing in the
"Greek Extended" tab.

Somehow, it did not occur to me that I need to select a different font.
Maybe, MuseScore could fall back to a different font when glyphs are
missing. But it is not a bug with the MuseScore packaging in Guix.

Roman