That’s most likely thanks to changes that Apple have made to Gatekeeper. See this post for how to fix: Can't find "Vocal Removal/Isolation" effect - #5 by steve
Depending on how old your previous version of Audacity was, managing plug-ins may have changed. See here for how to install and remove plug-ins in Audacity 2.1.3: FAQ:Installation, Startup and Plugins - Audacity Manual
and particularly this bit: Plugin Manager - Add / Remove Effects, Generators and Analyzers - Audacity Manual
That’s a bug in Audacity 2.1.2. I believe it’s been fixed in the development code, so the fix will be in the next release which is due out very soon (the “release candidate” RC1 is available for testing, about 2/3rds of the way down the list here: Audacity download latest version)