From my understanding (and I’m no expert, by any means) problem arises from GTK using mainly XSettings for theme info; apparently, KDE (Kubuntu, at least) doesn’t use it and, instead, rely on
~/.gtkrc-2.0 file, through KDE GTK config. The file isn’t exported to Snap by any desktop-oriented interface I know of - personal-files might work, but I believe it’s not meant to be used like this.
Don’t want to reinvent the wheel, so question is: is there a known, documented way of treating this?
As a workaround, user can copy
~/snap/prusa-slicer/current/, but this is suboptimal (linking doesn’t seem to work either, because of containment, I guess).