D’oh! I wasn’t thinking. Your license entitles you to previous versions of Cubase. So if you want the synths download Cubase 11 and move the file to the Cubase 14 folder. It’s VST3 so it’s in
C:\Program Files\Steinberg\Cubase 11\VST3
and is called SynthEngine.vst3
and just move it to
C:\Program Files\Steinberg\Cubase 14\VST3
You could uninstall Cubase 11 after you move the file if you want or need the space. If you do that, maybe save a backup copy of the SynthEngine.vst3 file somewhere, just in case.