If you have both GineverLauncher and Robbit Launcher 3 installed, and then you run the uninstaller for either GineverLauncher or Robbit Launcher 3 and leave the checkbox checked to remove additional data files, they are not actually removed. Unticking and reticking the box, as well as leaving it ticked, also do not work to remove those additional files. Essentially the checkbox does nothing. This basically renders the uninstaller almost completely pointless, since the additional files make up almost the entirety of the installed data.
This issue does not happen if you only have one launcher installed and you go to uninstall it.
Similarly, the issue also does not happen if you previously had two launchers installed, but you already brokenly uninstalled one of them and you are now trying to uninstall the other. Or at least it doesn't occur during the second cleanup... only the first. Meaning that if you uninstall both launchers, whichever one you uninstall last is cleaned up properly.
Current workaround: In the obscure event that you actually want to uninstall/delete the launchers and have both launchers installed, you can just manually delete anything which the uninstaller fails to uninstall after finishing the uninstallation process.