mixer lost MuseSounds after passing from 4.5.2 to 4.6.2

Issue type

Other type of issue

Description with steps to reproduce

My system is a Linux Debian 12.
My musescore installation (MuseScore Studio 4.5.2) was workinq perfectly.
Few days ago I downloaded the version 4.6.2 (namely MuseScore-Studio-4.6.2.252830930-x86_64.AppImage ) and launched it
As a first step, it requested to "upgrade" MuseHub.
I did it.
The MuseScore sreen opened as always but:

1. the museSounds option disappeared from the mixer
2. when I write a note to the staff clicking with the mouse, this operation is automacically repeated, inserting an infinite series of identical notes following the mouse position, until I close the window. (see the second screenshot)

These two facts remains even if I launch the old 4.5.2 version of the application, or a preceding one, 4.4 or so.
I tried some testing:
When launching MuseScore Studio 4.6.2 from a terminal I get, as always, a long list of messages. One of them is the following:

Instrument folder environment variable not defined! Add config file to /var/lib/MuseSampler/.config or Set "MUSESAMPLER_INSTRUMENT_FOLDER" and reinitialize MuseSampler.

The referred .config file contains one line:
/srv/muse-hub/downloads/Instruments/
which is not correct

I made manually the association exporting the correct path to the MUSESAMPLER_INSTRUMENT_FOLDER variable (~/.muse-sounds/manager/downloads/Instruments/ (this is the location where I found MuseHub placed them)

The complain message disappears, which means that the musesounds have now been found.
But now I have these two lines among the messages:

11:48:57.516 | ERROR | main_thread | MuseSamplerLibHandler::init | Could not init lib
11:48:57.516 | ERROR | main_thread | MuseSamplerResolver::init | Could not init MuseSampler: /home/bill/.local/share/MuseSampler/lib/libMuseSamplerCoreLib.so, version: 0.102.2

(see the first screenshot)

This shared library exists, the path is correct and it is recent (Sept 30th, many days before I upgraded MuseHub on oct 13th). At that date everything worked correctly

I don't know what to do
I suspect that it is only a problem of wrong paths and that the (many) .mscz files are unaffected.
In any case I have avoided to save the files when closing them, as suggested from Musescore.

Supporting files, videos and screenshots

In which versions of MuseScore Studio is this issue present?

4.6.2

Regression

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Operating system

Linux Debian 12

Additional context

No response

Checklist

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• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible