See screenshot please. I think there is no reason to keep "Launch" button visible and clickable during uninstall proccess. Both packagekit and flatpak backends are affected. I did not test Snap.
Created attachment 112443 [details] screenshot
Git commit f5ad3ff0ce40cb5bdefcc8e5ca21b9b85c2062ff by Aleix Pol. Committed on 07/05/2018 at 16:20. Pushed by apol into branch 'Plasma/5.12'. Hide launch button while uninstalling M +1 -1 discover/qml/ApplicationPage.qml https://commits.kde.org/discover/f5ad3ff0ce40cb5bdefcc8e5ca21b9b85c2062ff