I see you are using the desktop-qt5 cloud part, which should configure this for you by dropping a fontconfig configuration file in ~/snap/$snapname/current/.config/fontsconfig/fonts.conf that should make the fonts visible to the fontconfig system: both host system fonts and those shipped with the snap. Does that file look sane on the problem system?
The suggestion to symlink the snap’s fonts is just making the fonts available in a location fontconfig would otherwise search for them if it was ignoring that file.