The package updater in the Plasma system tray is no longer able to install updates. It will detect new packages, but instead of offering an install button it now tells you “run ‘zypper dup’ manually”.
This renders the update widget useless: It now does nothing but show you a list of new packages. Further more, the updater won’t even detect that you’ve installed those packages after you do run ‘zypper dup’ and will keep the tray icon active forever, making it even more of an annoyance as you need to restart plasmashell to get rid of the outdated notification.
I was told this might be a deliberate decision on Tumbleweed, as a normal ‘zypper up’ might leave the system broken (I never had that problem). If that is the case, my suggestion solution would be teaching the widget how to run ‘zypper dup’ on its own: It will need to ask for a root password each time you click install, but this is far better than disabling its update functionality entirely and leaving Tumbleweed users without an embedded package manager altogether.