I have several problems with the new KDE 5.12 on my laptop.
1) It is not possible to unlock widgets. Clicking the right mouse button does not do anything. There is no context menu: not on the Desktop, not on the panel.
a) I also tried keyboard combinations to unlock the widgets. It didn't work.dl I used the combinations listed here:
2) The System Tray has disappeared.
3) It is no longer possible to connect to wireless networks. I restarted Network Manager. It didn't help. I've since rebooted & logged in several times. It is possible to connect to the Internet via ethernet.
4) Clicking on the item that configures Mouse Settings (switching left/right buttons, scroll direction, etc) crashes SystemSettings immediate and without error message.
It is an Asus Vivobook X541NA. It worked flawlessly before today's upgrades.
Out of curiosity, I added a second user account. It had the same problems with the mouse.