fluidr3mono-gm-soundfont binary package in Ubuntu Focal amd64

 This is the hard disc space-saving Mono version of the complete
 Fluid (R3) GM SoundFont in the compressed SF3 format, as shipped
 with MuseScore 2.0 up to, but not including, 2.2.
 .
 It can be used with most modern MIDI synthesisers which support
 the SF3 format and has a low installed size footprint, while
 providing the large GM sound set. It does not, however, support
 Single-Note Dynamics with MuseScore 3.2 and higher.
 .
 As it comes under the MIT licence, it can be used in most settings,
 but do remember that waveforms generated using this soundfont are
 “copies or substantial portions of the” soundfont.
 .
 This package will be installed into /usr/share/sounds/sf3/ which
 is the standard Debian location for system-wide SF3 soundfonts.

Source package