Although I’ve moved the files shown in this screengrab to a folder in ~/Library/Application Support/RapidWeaver and zipped it so that - by my reckoning - none of these should appear as failing when I launch RW 8.7, I’m still seeing the message.
In the location you mention I also find RW related plugins BUT if I launch RW 8.7 and select the option to Reveal in Finder (via Preferences) I get a different location in ~Library/Group Containers/random letters.com.realmacsoftware.rapidweaver.
Maybe worth a look in your Group Containers folder?
That’s what I thought. So the obvious thing for me to do was what (I think!) I have: removed both those (and all the others which persist on showing up when I launch RW) from ~/Library/Application Support/RapidWeaver, where I have all my addons (which RW otherwise recognizes as I’d expect).
To my knowledge,
There is no plist or anything that RapidWeaver uses to keep track of plugins.
It is simply the location (that you can set) for the plugins folder. It then “Builds” the plugins on the fly at launch. If you disable a plugin, it moves the plugin to a folder called Plugins Disabled.
So what I suspect is RW is pointing to a different location than you think for the addons folder.
If you close RW down and reopen with the option key, you can disable all 3rd party plugins and get RW launched. Then I’d go to the addons manager and Reveal in Finder and check what is there.