[Linux] MuseScore Flatpack package unable to use Muse Sounds

Summary by @shoogle:

Muse Sounds works when MuseScore is installed as an AppImage but not when MuseScore is installed as a Flatpack.

It appears that the Flatpack package:

1. Is unable to access the libMuseSamplerCoreLib.so library at its default location.
2. Provides a different version of libopus to that expected by libMuseSamplerCoreLib.so.

These could be solved by:

1. Muse Hub installing libMuseSamplerCoreLib.so to a location that Flatpacks are able to access.
2. Using a static version of libopus, or a dynamic version with "custom mode support" disabled, or the Flatpack maintainer could bundle the version of libopus libMuseSamplerCoreLib.so is currently using.

Original issue content:

OS: Pop!_OS 22.04 LTS, based on Ubuntu 22.04
Musescore Version: OS: KDE Flatpak runtime, Arch.: x86_64, MuseScore version (64-bit): 4.0.2-, revision: github-musescore-musescore-

Issue:
After installing MuseHub and Musescore 4.02 from the flatpak, the Soundfonts (saved in the default location) are not found by the flatpak. If I install the AppImage instead (MuseScore-4.0.2.230651545-x86_64.AppImage), it does find the Soundfonts.

Steps taken:
Install Musescore 4.0
Install MuseHub and Soundfonts
Unable to access Soundfonts
Uninstall and purge Musehub and Musescore
Install Musehub
Install Musescore
Unable to access Soundfonts
Install AppImage
Soundfonts work in AppImage
Update Musescore flatpak to 4.02
Unable to access Soundfonts in flatpak

Currently I can access the Soundfonts by using the AppImage version, however I would prefer to use the flatpak, if possible.

Thanks for any help with this.

Image of mixer showing no access to Soundfonts in flatpak