Missing glyphs in MuseScore "Insert special characters" tool, despite the
fact that the necessary fonts are installed.

How to reproduce
****************

1. Install "musescore" package or start a guix shell with that package.
2. Open "MU 4.3" application from an applications menu or start it from
   a terminal with "mscore" command, or "LC_ALL=C mscore" to ensure the
   interface in English.
3. Click "Remind me later" to close the "MuseScore Studio Development"
   dialogue informing about the new version of the software.
4. Click on a white rectangle with a large "+" on it and a "New score"
   label under it.
5. In the "New score" dialogue, click on any option in "Instruments"
   area, such as "Piccolo in C". As a result, the arrow button
   brightens, click it to "add selected instruments to score". As a
   result, the "Next" button in the middle of the three buttons in the
   bottom right of the dialogue window brightens up. Click it. In the
   next dialogue window, click "Done". An untitled score appears.
6. In the main menu of the application, select "Add", then "Text", then
   any existing element, such as "Title", "Subtitle", "Composer", etc.
   As a result, that element is selected in the "Untitled score" tab and
   the "Properties" tab appears in the left sidebar.
7. In the "Properties" tab in the left sidebar, click "Insert special
   characters" button. The "Special characters" dialogue appears.
8. In the "Special characters" dialogue, click "Unicode symbols" tab.
9. In the list in the left panel of "Unicode symbols" tab of the
   "Special characters" dialogue, select "Greek Extended".

Observed result
***************

In the "Greek Extended" section of "Unicode symbols" tab of the "Special
characters" dialogue, in MuseScore on Guix System, only the glyphs for
the following Unicode characters are displayed: "άέήίόύώΆιΈΉΐΊΰΎ΅`ΌΏ´".
The rest of the glyphs are not displayed and nothing is displayed in
their place.

Please refer to the attached file for an example output of "LC_ALL=C
mscore" while performing the above steps and closing the application.
Notably, it includes multiple instances of the following error:
"EngravingFont::draw | invalid sym: 2975"

Expected result
***************

Most of the characters are expected to be displayed. A few missing
characters are expected to be replaced with some placeholder character,
such as a question mark in some shape.

Additional information
**********************

Installing a font package with a large collection of glyphs, such as
font-google-noto package, does not affect the observed result.

Running "fc-cache -rv" updates the fonts cache but does not resolve
the above issue.

Other applications, such as gnome-characters or gucharmap, display most
of those glyphs.

Trisquel has a different version of MuseScore, which displays almost
all of the glyphs and shows a placeholder character instead of a few.

Previous discussion:
https://lists.gnu.org/archive/html/help-guix/2025-02/msg00051.html

$ mscore --version
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
MuseScore4Development 4.3.2
$ uname -a
Linux desk 6.12.12-gnu #1 SMP PREEMPT_DYNAMIC 1 x86_64 GNU/Linux
$ guix describe
Generation 7	08 лют 2025 11:18:03	(current)
  guix 5674ade
    repository URL: https://git.savannah.gnu.org/git/guix.git
    вітка: master
    коміт: 5674adeb7579bdcfdb7342e6552f4735cd8f2afc

Roman