I am not trying to install Grasshopper2 to Rhino 6. I am just wondering if the the plugins shown in the PackageManager have some sort of Rhino version compatibility identification?
Remember that, on Rhino 6, there is no PackageManager command. You are running TestPackageManager. That early prototype has a lot of issues that were fixed in the Rhino 7 command.
In Rhino 7, you won’t get Grasshopper2 in that list.
-wim