Hello,
The ngspice simulator found one or more compatibility errors when I opened it from the schematic in my biasing circuit project (.zip file containing project and error message screenshot) attached), using KiCad v.8.0.6. Before attempting this overall simulation, I first tested each component requiring a non-built in Spice model in an individual test circuit to verify that each component’s simulation run worked properly.
double definition of a subcircuit, probably not critical when both are the same, one of the two is ignored.
rt1: there is a device rt1 (temp dependent resistor) which does not have a ngspice model.
J2: a device without ngspice model
There are at least others:J1, J3, J4 which are connectors. If you don’t want to simulate them, exclude them from simulation. Otherwise you have to provide a spice model.
If you don’t need U1, exclude it. If you need only part of the inverters, tie the other inputs to GND. Never leave CMOS inputs open.