Thanks.
Yes, those are the links I found. The second leads to https://forum.kicad.info/t/ngspice-28-for-kicad/10968/19 talking about linking the shared objects to where they are installed by the tarball.
I start kicad from the command line but the only output I have seen is Gtk related warnings. The shared objects are normally stored in /usr/lib/x86_64-linux-gnu/ on an Ubuntu while the tarball stores them in /usr/local/lib/