Hello,
could it be that the solution you found, had been somehow related to Ubuntu? In TDF released rpm packages there is no libreoffice-gtk3 package and thus you won’t find it anywhere. The functionality is (most probably you are looking for the VCL GTK3 plugin) in package libobasis6.3-gnome-integration-6.3.4.2-2.x86_64.rpm
(esp.: shared library libvclplug_gtk3lo.so
)
Hope that helps.
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