ngspice-30 is now distributed with the stable release 5.1.2 and all KiCad nightlies (5.1.2 and 6) for Windows.
I am not sure about the macOS stable and nightlies. Could somebody with a MAC check it out?
stable
https://kicad-downloads.s3.cern.ch/index.html?prefix=osx/stable/
nightly 5.1.2
https://kicad-downloads.s3.cern.ch/index.html?prefix=osx/testing/5.1/
nightly 6
https://kicad-downloads.s3.cern.ch/index.html?prefix=osx/nightly/
To get the ngspice version from inside KiCad, you have to do a trick:
Open empty eeschema window.
Edit a text box (T from the right column) and type in the following:
.op $ just a dummy command here
.control
version
.endc
.op just gives a simulation command, the .control section will return the ngspice version.
Now do Tools–>Simulator–>Run Simulation
and you will see the ngspice version.