As has been reported by TD221 in this blog, the ngspice installation in Fedora Linux is incomplete, as the code models are missing.
All modern subcircuit device models (OpAmps etc.) make use of these code models, so their absence will lead to error messages like
MIF-ERROR - unable to find definition of model a$poly$g.xu1.gb1
or similar.
An immediate remedy is to install plain ngspice (not libngspice) in addition to KiCad (see here). As standard ngspice is packaged with the code models, this will help KiCad/ngspice as well.
Discussions with the Fedora ngspice package manager are ongoing how to permanently solve this issue.