There’s a “Nyquist plug-in” available in the first post of this topic: https://forum.audacityteam.org/t/envelope-follower-ducker/47090/1
Read the next few posts in that topic for clues as to how to use it.
Up to date installation instructions are here: https://manual.audacityteam.org/man/installing_effect_generator_and_analyzer_plug_ins_on_windows.html#nyquist_install