On the openSUSE Nvidia page https://en.opensuse.org/SDB:NVIDIA_drivers under the instructions for YaST installation (number 6) it tells me “Choose the appropriate driver: x11-video-nvidiaG02, x11-video-nvidiaG03 or x11-video-nvidiaG04”. But YaST does not show the x11-video-nvidiaG02 as being available. Searches with Google find it but only for 42.3.
Try removing xf86-video-nouveau, which if no part of any NVidia proprietary driver is installed, should cause automagic use of the default DDX driver, modesetting, on restart of X or reboot.
Uninstalling Mesa-dri-nouveau had no effect. But removing xf86-video-nouveau did. The flickering stopped while using web browsers. I am eager to test video playing as soon as I update all the software on this new installation. I had never heard of the default DDX driver. Is this something new for Leap 15?
It became upstream default with server 1.17.0, which was after 13.2 but before 42.1. Newness goes farther back than I know, first appearing AFAICT as xf86-video-modesetting in 12.3.