Generic blank icon on .MSCZ files

Hello,
Files with extension .mscz are shown with a blank icon instead of the MuseScore icon.

System specs:
- Ubuntu 22.04.4 LTS
- architecture: x86_64
- windowing system: X11

Steps to reproduce:
- Download the Linux AppImage from https://musescore.org/en/download
- Ctrl+I > Permissions > "Allow executing file as program"
- Run ./MuseScore*.AppImage install
- Add this to .bashrc: export PATH=$HOME/.local/bin:$PATH

Result:
The app works, shows in Applications and in "Open with" with the MuseScore icon, double-clicking .mscz files opens them in MuseScore, but they have generic blank icons.

What I have tried:
- Open: sudo gedit /etc/mime.types
- Add: application/x-musescore mscz
- Copy SVG: sudo mv application-x-musescore.svg /usr/share/icons/gnome/scalable/mimetypes
- Restart

Still no icons.

I have also tried pasting the SVG in these locations:
- ~/.local/share/icons/hicolor/scalable/mimetypes
- /usr/share/icons/gnome/scalable/mimetypes

Something else I tried is to change the filename to mscore4portable.svg instead of application-x-musescore.svg for all three locations, since I saw that is the value of Icon in the desktop file (the one in ~/.local/share/applications/org.musescore.MuseScore4portable.desktop).

Another crazy thing I tried was setting both user:group to root:root and $USER:$USER on the SVG file.

Not sure what else to try, .mscz files still appear with a generic blank icon.
Appreciate any ideas or suggestions you can share.