i don't think any version of qsynth has ever worked under win98 due to fluidsynth's requirement for newer glib versions. it's possible to strip out glib from fluidsynth, but you can also substitute older win98 friendly glib versions for 1.x.x versions of libfluidsynth.dll. i found this out when i compiled my own win98 compatible dosbox ece build (with fluidsynth patch) from this post here: Re: DOSBox ECE (for Windows & Linux)

so if you install the qsynth-0.3.6-setup.exe binary still available on sourceforge (https://sourceforge.net/projects/qsynth/) that will give you a v1.1.3 libfluidsynth.dll. simply replace the libglib, libgthread dll libraries plus add the renamed v1.9.2-1 iconv.dll in the qsynth program files folder and you will have a fully functional qsynth environment under win98 (and probably later versions of win95). just add midi yoke and you are off to the races.

i tested all versions and glib v2.12-13 is the last release that will work under win98se.
https://download.gnome.org/binaries/win32/gli … lib-2.12.13.zip
https://gnuwin32.sourceforge.net/downlinks/li … onv-bin-zip.php