Would an "all controls" gang on the mixer help with overload problems?
I don't know enough about how the MuseScore mixer works to know whether this suggestion makes sense.
In the Mixer there is an overall gain control. However it occurs to me that the signals could be distorted due to digital overload before they get to that overall gain control. If that were the case, then it might be useful to have a way of controlling all the individual sliders in parallel, to avoid that kind of overload.
I am currently testing using the MuseScore OpenScore version of the Planets - https://musescore.com/openscore/scores/5271023 which can definitely drive my poor little computer into overload states - with distortion.
This may be unavoidable give the hardware we have and the current load it is trying to run.
There are too many** channels in the Mixer for this piece for it to be easy to lower the levels on each of them quickly - particularly if what is really needed is just a global reduction.
It would be interesting to have views and more information about this.
** Wouldn't it be useful to have a number for each channel, so that the total number of channels could easily be seen? Maybe there is that feature already - but I've not seen it.