UPDATE
It appears there are competing help articles. The one listed as “problematic” (below) was found via a Help Center search and is likely not linked into the navigation chapter lists.
This is the newer of the two:
Problematic URL:
https://help.sketchup.com/en/installing-ruby-plugins-extensions
Description of the Issue:
Out of Date from v2017 and higher. (Ie, still tells user to go through the Preferences dialog to control extensions.)
Selected Version of SketchUp:
2017 and higher
Selected Operating System:
Applies to both Windows and MacOS.