out of curiosity - Fluid question

IIRC because panning works properly only with mono.

The Fluid mono soundfont is mono only in that the samples used are monophonic. These are then applied to a stereo soundstage by means of the panning control, so you are not gaining any particular benefit by using the original.

The initial reason for doing this was to try and fix a panning issue, but in the end it emerged that our version of Fluidsynth needed patching.

During the soundfont modifications, however, I discovered that all monophonic sound sources such as saxes, violins, clarinets etc were all based on stereo samples, but the ones you would expect to be stereo, strings, synths, pianos etc were all based on mono samples.

The decision was therefore taken to continue using the version with mono samples in order to save bandwidth, and consequently disk/memory space.

The modified soundfont was named FluidR3Mono to distinguish it from the original, and is undergoing continuous improvements.

By reverting to the original you are not, therefore, taking advantage of the many improvements which have taken place in FluidR3Mono.

The latest SF2 version of FluidR3Mono is always available from the Soundfont forum.....
https://musescore.org/en/node/41521#comment-406311

The latest version having a (somewhat limited) Temple Blocks instrument added.

HTH
Michael (FluidR3Mono soundfont maintainer)

PS SF3 versions are usually released along with major updates of MuseScore, but are always behind the SF2 version. Notifications of a new release are also usually announced in the Soundfont Forum.