Upgraded to MacBook Pro Catalina

Not sure what might have happened

There really is no reason to “double-click” and reinstall every single add on.

  1. On the old computer, I’d make sure all the addons are up to date.
  2. Since you are able to find the old addons folder I’d copy that to the USB drive. Copy everything.
  3. One the new computer locates the addons folder and copy everything from the old computer’s addons folder to the new addons folder.
  4. when RapidWeaver starts again you should have all the addons.

https://help.realmacsoftware.com/en/articles/2237849-manually-copying-over-addons-from-rapidweaver-6-or-7-to-rapidweaver-8

Since you are running Catalina, some of the [older plugins may not work you should get a warning message about the plugins not being notarized… All the ones you have mentioned (Pluskit, sitemap, and stacks) all have versions that will work with Catalina.