After last KDE Plasma update [to 5.12.1] desktop is tearing on Nvidia GeForce GTX 1060 with OPEN-DRIVERS. Before update this problem didn't occur. On KDE Plasma 5.12.2 bug is still not resolved.
Created attachment 111083 [details] Open-driver is used.
Please give a try to the proprietary Nvidia driver. The free one still is not up to the task.