Assuming you are also missing Pluck and Risset Drum in the Generate Menu, please see this topic for solutions:
https://forum.audacityteam.org/t/nyquist-effects-missing/43925/9
I also assume you already installing Audacity correctly:
https://forum.audacityteam.org/t/installation-do-not-run-audacity-from-the-dmg/31711/1
Gale