I have seen “Ghost plugins” in Audcaity on Windows:
where plugins which have been deleted still appear,
because they are still on Audcaity’s “pluginregistry.cfg” file.
[I don’t speak Mac … Installing and updating Audacity on Mac - Audacity Manual]
NB: I would rename*, rather than delete Audcaity files/folders, so you have the option of going back to how it was.
[* e.g. rename “pluginregistry.cfg” to “pluginregistry-old.cfg” ].