Ahh, I hadn't seen that tool yet
You can ignore the warning for the JFBConnect auth, system and user plugins. Looking at the descriptions on my test J4 site for that tool, it looks like it just doesn't know where to fetch the updateserver information for those plugins. We just put the update version info in the top level JFBConnect package. When you install the JFBConnect package, all those get updated as well.
I will put an item in our to-do list to investigate fixing the warning in a later release.
-Melissa